I'd love to have an updated UI where I could just right-click to close inventory and menus, instead of having to click directly on the checkmark. If a mod like that exists for Exult, I haven't seen it in all my searching.

If I'd be making a remake of early Ultimas, I'd use an engine like Original Sin games. It actually might work as it is for Ultima 1-3, from 4 upwards you'd need a NPC schedule system.