I see... Very good points, I'd say. also, I DID say that we only know for sure that the 1:1 ratio only applies to the primary session IE the seeded sessions. In the story itself, it's been implied there were other sessions, like fedorafreak's session, or even that that one football player may be part of a session where his own dreamself died. There is a LOT of flexibility. Although, the crossing sessions thing needs certain requirements to be met, though it shouldn't be too hard to pull off, with the proper information. There's a lot of room to explore an expanded universe. The problem with a 5th type of session, though, is that the conditions for each session type are pretty clearly defined, aside from minor differences separating successful and standard null sessions. There really isn't a lot of room for exploring a non-standard session type, since they are very much dependent on the conditions surrounding entry into the session (not counting the VERY abnormal conditions of Homestuck's own setting. But again, that one is also (somewhat) clearly defined). The only way I can think of around that is to find an entirely new way of entering a session that still designates you as a player through the game itself. ...Which is something you probably did. /rant
Anyways, yeah, I never thought that having a vampire in a session would be too farfetched, considering rainbow drinkers. It has been stated that the abilities you get in the game are not the only ones you can use to win. You can use any other abilities you get through any means, be they racial abilities, like cherub planet-killing energies, or Vriska's mind control, things acquired through unusual circumstances, like John's new retcon ability, or even having your essence or something corrupted, like grimdark!Rose. I shall not even mention Trickster Mode outside this sentence. Point is, anything goes ability-wise. /rantagain
Ectobiological cross-species hybrids are a bit of a stretch, but not unallowed, IMO. I was actually thinking that multi-species sessions could be a thing in an EU session. Just don't make a sue is all I can think to say.
TL;DR version: I think uneven gender ratios are okay if it isn't a seeded session, a new session type requires some serious world-building to be acceptable, vampires are okay, along with any kind of innate or acquired superpower (just don't godmod), and hybrids are okay so long as they aren't Mary Sues trying to be the most important character.
Also, I wanna be a Lord of Heart.