- The Music
- The Voices
- The actors in the FMVs
- The hotkeys (allow them to be remappable)
- Modding and Mapping capability and tools. People want to be able to mod and map the game. They want to add 3rd, 4th and 5th factions with new unit & gameplay mechanics, their own UIs for the new factions, etc. - Let them do it, please! That's how the C&C Community survived for so long.
- No paid content, even if it's skins, only. Skins could be an extra thing for pre-ordering and for the collector's edition, but that should end there. Skins could work in a new C&C game, but I can hardly see it in a remaster, especially if it's one of the 2D games like RA1, TD, TS and RA2.
What can be changed:
Adapting the UI and more varied and modern waypoint, build queue, unit pathfinding and formation mechanics from C&C3 and such can work, but the rest must remain the same. It could work if you had a classic mode like with DTA, for example. In classic mode, GDI and Nod have their original TD arsenal but in "Enhanced mode", GDI gets Hover MLRS, mechs, Nod gets subterranean beam cannons, cyborgs, etc. - as well as an additional tech center, to lengthen the build orders and tiers. Maybe in "Enhanced mode", you can build several build queues ala C&C3 and RA3 instead of each subsequent ConYard, War Factory or Barracks simply speeding up unit production. I can see that work. The art style can be changed to 3D with a fixed camera in classic mode, but enhanced mode lets you maybe rotate buildings ala RA3 and the camera, as well.