Vampiric Suggestion
1. Treat potions of blood as permafood. Potions of blood coagulating and being different than normal potions is a little weird.
2. Drop the level six 'bottle blood' ability; because it's a tedious action now and considering (1) would be infinite permafood.
3. Add a selection of Vampire/Crypt-themed vaults to spawn D : 20-25. This is to serve as a 'blood bank' for the end-game bloodless floors, still a limited supply, but a supply (like the permafood supply given mid-game to regular characters). Should include a sizable stack of blood potions and at least one blood fountain with a reduced (or non-existent) dry up rate. Be nothing but a small selection of Out-of-Branch enemies to non-vampires, but very helpful to vampires. Set it so one -must- spawn for vampires and has the same chance as normal vaults for non-vamps. (Could also potentially place a blood vault in Crypt: 1, but that would require making it through some corpseless/bloodless branch to reach.)
Thinking behind this is fairly simple; if stuck in bloodless for too long (which can happen on corpseless floors in mid-late game), the player is likely to wish to SCUM (which is possible with no strict [death-causing] food clock) in order to find blood in order to regenerate. This would offer something to prevent that behavior (a late game blood supply that stays there) and provide for a means to regenerate (and attain alive status) in the hells/abyss/etc. Though as limited as normal permafood or more so.