The BI exe seems to support everything that was in the original. I've been playing my current campaign for 180 turns and all is well.
As for the Imperial campaign. It won't work through it's original menu slot but will appear in provincial campaigns and seems to work fine.

To run RTW through the BI.exe you should make a shortcut to the BI.exe, right click on it and go to properties. Add -mod:Data to the end of the target line (leaving one space between) so it looks something like this:

"C:\Program Files\Activision\Rome - Total War\RomeTW-BI.exe" -mod:Data

The new BI unit abilities like shieldwall, swimming, ect... can now be activated using the appropriate tags in the EDU.
The night battle, hording and sacking settlement features will require a bit more work.

I activated the night battles using this great tutorial: https://forums.totalwar.org/vb/showthread.php?t=59950

Peace