I have some concerns on how compatibility will be with existing fan missions since there's already been a recent debate over unofficial engine versions and missions that require the most recent community patch vs older ones. But nonetheless it will be good to have an official release that actually works on moderns systems out the box. I believe the previous steam ones were never fixed, just GOG's.
I can go either way on the updated visuals, especially from the looks of them touching the hand drawn mission briefings, but I think they may have some updated, uncompressed audio for sounds and ambience for this and I would really appreciate having that. Always been one of the strongest parts of the series as is.
Total shot in the dark too but I kinda hope we can get some of that unstable multiplayer support from Thief 2 fixed up for this. And ideally if all goes well and they get to Deadly Shadows, they just gut and redo the movement on that one entirely.