The game was already pretty damn sharp looking even when I played it last year. Looking like the most they've done was add more geometry detail to the characters (rounding some edges, adding more hair detail, etc), which was about all you could really do with how well the original nailed the comic book aesthetic. Maybe clean-up some of the Telltale animation jank (odd transitions, or the 1-frame hiccups) while you're at it.
Spoiler: show
I guess they could try to improve the lip-sync/facial animations to be more up to modern game standards, but that'd be such an expensive task for a remaster, especially for a game which is 90% listening to spoken dialog.