Is there anything I can do to get around the 150 device limit using the Built-In HomeKit Integration for Hubitat? I know I can go above this with Homebridge, but I do like how integrated and seamless it works with the hub and would like to avoid having to go back to Homebridge again.
Not a good answer, but you could get another Hubitat hub and put some of your devices on it. hub mesh to the other hub. Create new HomeKit Integration from new hub.
Important to note that hub meshed devices are not allowed in the inbuilt HomeKit app. For this reason I still run HomeBridge because of my multihub setup.
And that is why you need another "connector" from the new hub.
I swear I was able to do more than 150 with Homebridge, but maybe not? If it's a HomeKit limitation then I guess there isn't much I can do by adding another hub or another bridge instance. I'll just use Groups and Scenes or Room Lighting to consolidate some things. Like I have multiple Wifi Outdoor Plugs for my landscape lighting outside. I can just make a single device in Hubitat for multiple plugs to get around this I guess.
HomeBridge can create multiple "child bridges" to work around this limitation (among other reasons you may want to separate things) as of an update a few years ago:
If you had more than 149 or 150 devices, that is probably what you were doing.