Ah, that's disappointing. :/ Do you think there's any chance this feature could be added? I know that Emulation Station/ES-DE has that feature, and I can't imagine it being too hard to code in - without having any knowledge of mGalaxy's source, I imagine it'd be a filename check to see what video is currently playing, then if button "accept" or "X" or "A" is pressed (however you want to define it), check for the matching ROM file based on the filename, and launch the appropriate emulator as normal for the ROM.
I'm sure it's slightly more complicated than that but hopefully not too much so?
Likewise, is there a "next" button so that if I pressed right or arrow key right, it skips to the next preview?