Re: The infamous "Resuming" screen, any chance windows 10 for "phone" gonna fix that
Optimization for what? Apps or the OS?
Mostly OS, and this in return will apps too.. If LongListSelector in WP8 has issues then every app using LongListSelector will have issues. This inheritance can extend all the way to the lowest level parts of the OS.
Microsoft has confirmed multiple times that they are neglecting the S4 platform that the 820/920/1020/etc were built on.
There are no S4 devices being manufactured in the future so it would be safe to assume that W10 was targeted for the newer Snapdragon SoCs. Qualcomm has solutions that Microsoft uses too, that are extended/removed/etc.
E.g this would be impractical to implement on a Lumia 1020:
https://www.youtube.com/watch?v=CaS0kpozyMM#t=20
As features are being added and enhanced it is easy to create two divergent development paths, similar to Lumia Camera and Classic...
W10 was built on top of WP8.1 so it is safe to assume that S4 devices are compatible with core OS functionality.
Ultimately: If WP8.1 app compatbility is a concern, older Lumias are a good candidate for Loading/Resuming screens. Not saying that the 1020 is slower than the 830, because it is definitely not, however it is reasonable to assume that Microsoft will not be doubling down development for a platform that is no longer in production.