I see two, maybe three tags from what currently is aliased into "invalid tag" that could be aliased into something else:
furryfandom -> furry fandom
anthro art -> anthro
and maybe the third one could be:
adorapipp -> pipp petals (mlp)
> Most of the Fluids tags seem like they should instead be aliased to something (not sure what is the right tag), rather than invalid, and probably Anal Play as well.
I can imagine somebody using "anal play" for both sex and masturbation and I don't see other candidates except "explicit" for both of them, but more on that below.
> And then the furry ____ seem again great targets for aliasing. Furry Art might be a bit vague, but “furry Porn” and friends could just default to “explicit”,
We don't do aliases or impluications into rating tags, it would create the possibility of having not acceptable combinations of tags, like both "questionable" and "explicit" could potentially be present on one image. You can't manually add them both, but it's possible to end up with that with an alias to rating tag.
> “furry girl” is just “anthro” + “female”, “furry and pony” is “anthro” + “feral”.
Unfortunately there is no way to currently alias one tag into more than one tag.
Another thing to consider is also how suggestion system works with fancy tag editor enabled. If for example "furry girl" was aliased into "female" then after typing "furry" in tag editor the first suggestion would be "female" as this tag has the most images under it.
You can observe this for example with the "weapons-grade cute" being aliased to "cute", when typing "weapon" in tag editor the first suggestion is just "cute" which looks strange and is unhelpful.