this is really doable on a personal level!
I have split my collection up via US & Euro releases and Japanese releases, (I’ve even gone as far as separating Hacked/Modded Roms & Tanslations) that’s much similar to your separate system idea/needs
you just need to edit your es_systems.cfg accordingly and then create rom folders for the systems you’ve added to the es_systems.cfg
then it comes to theming, I can create some custom ones if your using my theme? (it’s posted in the themes part of the forum)
Wow, that’s really great that this can all be configurable. Your idea for separating rom sets by region and translated roms is something I would also be very interested in. I’ll definitely take a look, thanks!