I understand the intent was that it was to be easier for all manufactures to use one specification. I think what I meant was, how many users would have Apple, Google, Samsung, etc. all at the same time and need to control the same device from all of them. I realize it could be done, but do you have an Apple Ipod in one room and Echo device in another and Google device in another. And depending on what room you are in do you say Alexa, Hey Google, etc. Just being facetious here but trying to explain what I meant.
...yes. 
Echo in living room, Google Homes in office and family room, home pods in garage and other end of living room. I have friends/family members w/mixed ecosystems due to when/how they started into HA and family member preferences (iOS vs. Android).
I think the idea was that you would not have to worry about what brand gear and controllers you have, they would all "just work" and you could control things from whichever hub/controller(s) you wanted to, not be locked into one or another, which can be frustrating. Not everyone's key issue, but seemingly enough that Matter targeted it w/their design/marketing.
Ok, do you have the same matter device paired to all the systems? Or do they just interface to HE?
Please don’t take any of my comments as being negative, I just like to understand.
As a user, I have Apple Home, Google Home, Smartthings, and Hubitat as my Matter controllers. Almost all of my Matter devices are generally in Google Home (for voice control) and Hubitat (advance automation). Apple Home and Smartthings is very dependent on the automation, but I also designed my smart home around the idea of my family being able to modify as they deem fit. So, some automations live in Apple, Google, Smartthings, and Philips Hue app with Hubitat serving as both an advance automation overlay and easier logging insights. Matter fits really nicely into my goals for smart home design, but like most of us on this forum, I/we are unique in this space.
As for your more specific question, it is highly doubtful that most non- "Hubitat/Home Assistant/Homey" users care a whole lot about Matter. It's just another tool when we "power" users make a decision on what device to use. It could be Matter, Zigbee, ZWave, etc...depending on the automation hub.
For more regular users, they are most likely to have one of Apple, Amazon, or Google for their voice/automation controls. The benefits to manufactures also help these more regular users as "theoretically" they can look for the branding "Works with Matter" and generally know that it will work with their preferred system. One could argue that the marketing differences between WiFi and Thread need to be highlighted for easier understanding, but that is something slightly different.
I think this is what I was trying to get at and not do a very good job of it.
Most folks here are probably more deeply involved and are the exception.
Good discussion, thanks.
Absolutely, we are the weirdos on the edge most definitely in many of these areas. 
One of them did drop off Home but I now think it may have been a battery issue, which itself is odd because they were newly charge IKEA batteries installed just a few weeks ago.
I've wiped the slate clean and adding things back to HE again and plan to diagnose more carefully.
Judging by their ZigBee record they will get there, eventually. 
LOL...so you're telling us "Patience, my young padawans..." 
Yes and no.
I think it's useful ponder that question over a timeline, not just "in the moment". Over time, a preferred system may disappear, become obsolete or you might decide a new system will work better for you. You might want to manage the transition without loss of function. Interoperability helps in those scenarios, too.
Absolutely. I am on, I think, my fourth system. And if I was to change again the fact that Matter is, or should be, compatible would hopefully make the change a whole lot easier. But in general the devices would only be on one system at a time.
EDIT: To clarify my usage, which may or may not be like anyone else. I have one system to control my 'smart home' (sometimes not so smart). The only reason I have other systems is to provide a better inteface to it. For example, Google Mini's for voice control. No matter devices directly connected there. Apple Home started out as mainly a much better phone interface. (Apple's Home Widgets are light years ahead of HE's). I can open the HOme app and turn something on/off while HE's app is still thinking about it. Then I had to use the Apple Home to add Matter devices originally then add to HE. With latest HE firmware that I understand is no longer required. But still need Apple to add Thread devices as HE can't. But in essence all devices are only paired to one system.
EDIT 2: By the way, I'm enjoying the heck out of this discussion. Learning a lot and getting ideas. Keep it up...
A little confused about something. Should you be able to add a Thread device into HE without first adding it into Home or some other thread router?
Reason I ask. I have one of the IKEA contact sensors that I don't have a use for. At one time I added it to Home and it worked there. I tried adding to HE from there and it added but just like the other stuff only worked for a short time. I removed it from Home and HE and reset the device and put it in a drawer.
Today I was fooling around, got it out. Put in battery and it went into pairing mode. I opened HE app on my phone and I was able to pair it to HE directly. Only worked for awhile before bombing again. But it was never in Home or anywhere else that I could find.
I was under the impression that a thread device couldn't be added to HE first, but maybe I didn't understand. I'm on a C8 not pro.
Did you factory reset the device or just removed it from Apple Home? Those are technically two different things. If you only removed it from Apple Home, the device keeps the Thread Network information which is similar to how the HomeKit Controller integration works. If you fully factory reset the device, it would have lost the thread network information and not be connecting to the network.
It was factory reset.
Just an updated data point two months later. These MYGGSPRAY sensors still are dropping off after a couple days as seen from Apple Home, so it isn't a Hubitat issue. If I power cycle one, it will work for a while and then stop.
The GRILLPLATS smart plugs are still not available, and maybe thing will be different after I add several of them to enhance the connectivity. But I'm not confident. One of the MYGGSPRAYs that drops off is about 10' from the Apple TV which now sits on top of the home entertainment center. As I believe I may have mentioned, I got a couple Onvis plugs to help but Thread isn't using them for routing.
I’ve got 2 of the MYGGSPRAY that seem to be rock solid. One Apple TV and one Apple mini pod for thread routers.
I don’t have them paired with HE as that never seemed to work right. Just feed them to HE thru a virtual switch and Apple automation.
For me, 100% of the instability was related to the fact that a Google Hub Max that was on my primary VLAN was a TBR, and devices would jump to it and away from a TBR that was on the same VLAN as HE. And you CANNOT disable the thread radio on the Google Hub Max.
Since then, all of my IKEA Matter over Thread devices have been rock solid.
Do you have them paired to HE? Every time I tried that they would work for a short time then quit. They always stayed working in Apple Home.
I just have a simple network no vlan’s or anything.
Sorry this is a bit off topic, but I think the sensors and other smart items are just a symptom of deeper issues at Ikea. I am not sure exactly what is going on with them lately.
A lot of stuff from Ikea is trash or non-existent right now. They have discontinued long standing lines of furniture and textiles. Their online catalog looks mighty thin for common stuff like sheets, rugs, and other common household items compared to the past.
I have been shopping there since the early 2000s, and I have many things like curtains, towels, and book shelves that have been very durable. Much of these household items I am still using 20 years later. I doubt their newer stuff will last me that long.
I tend to disagree. I have several motion detectors, contacts, and push buttons. Never had any issue with pairing them with Apple Home. (Don't know about edge hubs). As near as I can tell the quality seems to be on par with most of my other stuff.
The only issue I have is they don't want to work with HE. I can pair them with HE and they work for awhile and then quit. So by using Virtual switches and Home automations I have them integrated into HE.