I'm always a bit skeptical of projects that seek to harmonize or standardize APIs across different kinds of hardware devices, not for the benefit of users, but for the benefit of software developers.
The visions behind such projects often seem to produce elegantly designed software platforms, like Windows 10 Mobile[a] and Ubuntu Touch[b], for which there is actually no user demand.
Did end-users, i.e., regular people, ask for Project Reunion?
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[a] https://en.wikipedia.org/wiki/Windows_10_Mobile
[b] https://en.wikipedia.org/wiki/Ubuntu_Touch#Ubuntu_Mobile