Ok, so I've done a little preliminary investigation into modding, hopefully this might spur some interest.
Portraits can be injected at /Android/data/com.beamdog.baldursgateenhancededition/files/portraits
Game assets are located in a pair of files at /Android/obb/com.beamdog.baldursgateenhancededition/
; these can be extracted and modified with 7zip. The dialog.tlk is not identical to the current Windows release, but that is probably because the current Android version is 1.3.1226.
The game does not load anything other than portraits and probably soundsets, and maybe scripts (bs) from the .../data/... location ignoring any other directories (no override, etc). It also will not load scripts (bcs) or a dialog.tlk file from those locations.
The two obb files are interesting, though. The second one, beginning with 'patch' appears to be exactly what you might think it is - a zip of a partial directory structure we are very familiar with. Due to the way that android deals with this file, we don't get to do something as simple as add a new patch file with a newer version code; there can only be 2 obb files in this directory, and there seems to be some sort of error checking on both, so you can't simply inject changes into the patch zip.
Based on just a couple hours of fiddling here, I don't see any modding being possible unless we get override loading from .../data/..., both override directory and tlk's. If we can get that, though, the existing modding infrastructure should work just fine, and not even require a rooted device. If not, well, I'll try to disable the CRC on the patch file for my personal use, but I doubt distributing that would go over well, heh
to see if some attention could be brought to bear on getting proper override support. (Even a 'no' would be great, tbh.)