Update: Polygon Source Info in OP - Kotaku: Xbox Slim This Year, More Powerful Xbox One In 2017, Future Titles to Release on XB/PC, Iterative boxes from now on

[Goatseye]

PotentHerbs said:
Terrible that both Sony & MS are both pursuing an upgradeable model for consoles.

They haven't stated if they're modular, hell, they haven't even chimed in on the rumors. 

These boxes will still be closed and game development shouldn't be an issue because it should be the same to develop as their predecessor.