I love both versions of Baldur's Gate, thanks to each one having a different feeling and atmosphere, even if they are the same game. There are some things in the original version of Baldur's Gate that Overhall could easily update; a few examples.
Openal sound conversion: Overhall already did this for E.E., but why not easily add it to the original?
Very easy bug fixes: Ones that Overhall can quickly fix since they have full access to the game.
External saves: All saves and configurations are saved outside of the game (in "My Documents" on windows
version); like openal, Overhall has already done this with E.E. Doing this will make transferring the files less of a headache.
I know some of these are easy fixes while others might require extensive code modification, but releasing official updates to the original version would players experience them better.