It would work if the event fires reliably. The event would also have to change a ROS Card state that is available in HA.
I would prefer to be able to change the harmony activity from the remote and then the remote follows based on what the current harmony activity is. Enabling Harmony Activities to be sources would achieve this easier.
EDIT: Harmony Activities can already be mapped to Source/Application drop down.
So far so good. I have been able to recreate the activities…totally removing the Harmony from the system. Still tinkering but I have the basics of power on/off, input switching, source navigation and volume control.
Having one issue with my GE smart Air Conditioner…I have added the ROS Climate card but it never shows up on the remote…did refresh several times.
From what I recall, Global Caché is really helpful here, but to integrate it with Home Assistant you’d need to use a Homebridge plugin supporting devices like the GC-100-12—that takes care of both RS232 and IR control.
I used this hardware over a decade ago and it worked great. Obviously, I wasn’t running Home Assistant back then, just a Philips Pronto (that thing ate Logitech Harmony for breakfast back in the day and honestly remains unmatched even now).
Regarding your point on pushing volume info, channel status, or any entity to the Astrion screen: Are you suggesting a dedicated, custom display ROS card (or Widget) where users can bind arbitrary HA entities (like current volume level, media channel, or sensor states) purely for state visualization on the remote screen?
If so, could you share a bit more about your ideal layout or use case for this card? We’d love to make sure we design it in a way that fits seamlessly into your HA workflow!
Sorry for the late answer, I got swamped with work 
I guess, the most flexible thing would be to have something like a configurable dashboard either in grid form or if you want to be fancy, even more flexible where we could display widgets that show entities and, if feasible, react to touch - like, values, buttons, selects.
Something like what you can get with Mushroom cards now or the aforementioned Appdaemon/HADashboard. I’m aware that the hardware is too weak to run a fullblown browser that can display Lovelace reliably, but maybe restricted/stripped down or dedicated.
Then people could create their own interfaces instead of having to make do with the limited number of cards now available. You’re implementing more and more types of ROS Cards, sure, but those cannot be mixed on the display that IMO could handle much more than a single Entity even if it’s a media player.
