Holding money on a phone/watch should simply have two variants:

-Fully featured easy UX with node/lightning/mint in background (with thought-out failsafes)

-limited good ux but tiny data footprint

I wouldn't say it is the goal. Complete freedom and self custody is always the goal. But I do think that this is a realistic outcome, and I don't believe it would be due to technical challenges. Most people don't want that level of responsibility that comes with that freedom.

If one day it becomes clear that 250M+ are trying to use base layer Bitcoin, my perspective may change.