Possible monthly event: Obscure Map Day

[warcrimes]

The only downside I can see is keeping the old mystery maps up to date. And if they are up to date why are they not in rotation?

This concisely hits the nail on the head. 
The level of effort required to keep them playable is high, and our seven main maps are already suffering somewhat. 

Now, all that said, there are mitigating factors.
Using the correct placeholders can help with portability, and a healthy lowering of expectations also helps. 
I don't think we have the manpower to get the deprecated maps up to "regular" playable standard, being feature complete and all - but, i *might* be able to bodge one or two up to the standard of "It compiles, that's all you get" for the upcoming AssJam13.
It won't be Cogmap polished, but it will more or less run. 
If that goes well, who knows what's in the future for gimmick maps?