Late reply to this thread but figured it was worth bumping, I just released v2.1 of Emperor Reborn with proper Hor+ widescreen support, which based on my research nobody has actually pulled off before for this game.
Camera projection patched at the matrix level, UI re-anchored to screen edges, FMV cutscenes pillarboxed separately so they don't get stretched, tested at 1280x720 and the sidebar and minimap stay where they should be, you actually see more of the battlefield rather than the stretched or cropped mess from the old registry hack.
Release: github.com/azmawee/EmperorReborn/releases
Install guide and FAQ: azmawee.github.io/EmperorReborn
Built on wheybags' patch foundation, credit to him for the original Windows compatibility work that made this possible.