Well, [@UltikanaRe], if you look at the popup text on the "Historical tag", it says "Events of the past or an alternate one", so we'd say alternate history is covered. 

Some form of tags for marking whether an RP is utterly original, inspired by something or a full-on fandom would also be useful, [@Sage].
A bit of a discussion on what each of them should be is something we think would be very helpful. As would comments on the tags currently listed as suggestions in the OP.
We cleaned up that list a bit now.