I asked the same thing during WWDC22 Labs and the API behavior and design is pretty much on lock down.
Taking hints from the system and the use cases that Apple has demonstrated, a package delivery, a sports event score change, a ride share service, these are all things that seem to be remote server updated. Meaning the phone can't do them on their own. Maybe you could do a conference planner/scheduler Live Activity that is all locally cached, but the use cases were telling to me. I have to imagine it will look like WidgetKit but have some aspect of content-available push that maybe goes right to your widget / live activity extension. Or to your app and then reload timeline if truly like widget kit.
I'd also bet that just like widgets on home and Lock Screen, Live Activities will be 100% SwiftUI for visuals. So my vote goes to learning "systemMedium" widget family, and SwiftUI. If you make a systemMedium Home Screen widget visually, hopefully it would be reusable for your live activity view.
Out of curiosity, what is your use case? How often would you want to refresh the live activity? This was also something I talked about in my lab, trying to get info on refresh policies--nothing :) Guess we will have to wait. I was encourage to #filefeedback on my ideas for Live Activities so Apple can see what we want to build.