To begin, I'm only here because I had someone complain to me about the vanilla conten for this wiki, so I decided to take a look. Since you (the current staff) are doing a pretty fine job, I'll give you some advice. (I'd suggest looking up my post history as well and then decide whether I'm worth listening to or not.)
I do realize that none of the current wiki-staff was involved in the that mess, and honestly, so don't take that as a personal stab, please.
Uhm, yeah... the irony kinda bites, when the biggest reason for the initial state of this wiki was KEEPING the vanilla and rebirth on one wiki and now you'd want to split it up once again?
You took over knowing very well what was expected of this wiki, so it's a bit weird trying to do the very same thing just because you're drowing under the work involved with having multiple page versions, something you should have considered the moment you considered adopting the wiki. Such is the burden of taking over an already established wiki.
Here's some arguments against a split:
- Your wiki loses a huge chunk of vistiors as you the wiki drops it's main alure. The current gamepedia wiki has you beat in numbers and community establishment. Sorry, that's a measurable fact, even if this makes me sound like a prick. (Since juggling with internal data in public is not a smart idea, here have something less accurate, yet telling and compare: https://www.similarweb.com/website/bindingofisaac.wikia.com to https://www.similarweb.com/website/bindingofisaacrebirth.gamepedia.com)
- You are currently operating under a mixed game version article system, and you have not properly labled everything specific to each version of the game on each page. So you'll have to redo those pages, as you need to split each article from the original and comb through which things are true for which version. That's truly a lot of work...
- You'll have to delete and reimport all related images as well.
- Do you have enough people to keep both wikis running at all? Vanilla's Eternal update still has a lot of things missing.
- This one is tangentially related to the discussion: Antibirth. Do you have the manpower and knowledge to keep that one correct and running? How do you handle version specific differences?
That's my 2 cents on the matter.