As I mentioned before, Home Assistant does work as a means to bridge Insteon to Hubitat for automation. And it will work with your PLM by adding a serial to USB adapter. It’s just not as responsive as the integration that’s been built by the community for Hubitat. Having said that, I don’t have a PLM, I have the Insteon hub. Maybe Home Assistant’s Insteon integration works better with the PLM than it does with the 2245-222 hub. 
Home Assistant does also have an ISY integration that I completely forgot about until now. No experience with that.
Either of these could be brought into Hubitat using a community built, super easy to install and use app/driver combination named Home Assistant Device Bridge. This is what I use for many other devices that are not currently compatible with Hubitat. Complex automation is definitely much easier on Hubitat, but if you're not looking for anything more complex than what you can currently do with ISY, it's possible Home Assistant might actually be all you need. It's just that when you want to create more complex automation or do something like comparisons to reference sensors, you will need to edit the Home Assistant automations in YAML, which really sucks. Some use Node Red for automation, which bypasses both Hubitat and Home Assistant for that task. But that's a new learning experience that will be much less familiar than what you currently do in ISY.
I like having both multiple hubs. Keeps my options wide open and allows me to use the hardware I want, instead of what's available on the menu. Not a choice everyone wants to make though, and I do understand my willingness to run multiple hubs and bridges is outside of the populous norm.
