But I am especulating that it won't be. At some point there will be design decisions to be made around trade-offs and I'm sure Google's necessity to push "ambient computing" into the world will prevail over any modularity concerns.

Or "ambient computing" is just marketing fluff, and in the end it will just be the same typical set of libs, and APIs and tools as in RN and other such frameworks, just with some extra UI widgets and libs for smaller devices.