It's not as simple as "just make it widescreen", guys. The engine wasn't originally coded to render an area larger than 4:3, so there could be issues trying to expand the screen size, like unfinished areas that would've been hidden off-camera suddenly being visible in gameplay and during cutscenes, and in-engine camera shots not working correctly due to some of the maths potentially being different. A screen hack for the Dreamcast version running in an emulator showed quite a few problems like those, like in big parts of the intro.
It could be fixed, but GungHo would need to retest the entire game, find those problems and fix the assets/patch the code where necessary and then retest the entire game again, multiple times, until everything is working. That's going to take time, if it happens at all.
Considering the status of the framerate is now exactly the same as what Ubi managed with the old PC version, I've got a sneaky suspicion that there's something framerate-dependent in the off-battle portions that makes it fuck up horribly if the framerate is unlocked there...