Instead of the "gender spectrum", what about the "gender continuum"?
"Continuum" keeps the "not a set of discrete points" part of "spectrum" without keeping the linearity (which many object to); continua can extend in any direction and even be multidimensional.
I see a bunch of people are already making jokes about that first toot but "spectrum" is already criticized for being linear and not including people who don't fit neatly anywhere between the "male" and "female" endpoints.
@noelle I like "continuum" but I'm not sure it's commonly considered multi-dimensional. It seems like it has more flexibility about ends than spectrum but it feels very similar. I tend to think of "plane" re: gender (a straight line in some random spot on it for a lot of folks with others off at various angles) but that doesn't quite work either.