Ill be honest i haven't been able to try the beta for the new MegaGlest, I don't remember seeing this listed as a change but i could be wrong...
Have the faction preview removed in a recent revision or did i disable it somehow? I do not have one. I remember there being a lag issue. Either way Here is a small thing we can add/change to the Custom Game screen.
Instead of using the faction specific loading screen during the Custom Game menu how about a separate smaller image perhaps 64x64 that would represent the faction as its symbol. It would be faster to load and would actually look better than a rescaled loading screen. Since a loading screen would be bigger there is plenty room for lots of details and actions, which could be lost into a blurry mess when re sized into that small box. Plus this way, you can have one "icon" per player (or cpu) which would look better instead of a single image on upper left. Many RTS in particular, multi-faction ones use a symbol next to the name, sometimes just a symbol instead of name.
Just an idea