It'll never happen until we get actual decent 3rd party cross play because the usage percentage of people actually on these things is so incredibly small, it's not worth anyone's time or money to detect.
Doesn't help that you have a vocal minority complaining to developers that crossplay should be removed or cancelled from upcoming games because of this issue.
I don't know of any games where I'm playing against PC people with a keyboard mouse while I have a controller. So yeah, I don't think crossplay is anything to do with this, and I don't think that ever will, there is no way a developer will do crossplay for a first person shooter, for example.
Usage - yes, It's incredibly small, but doesn't mean it always will be. Call of Duty devs have mentioned detecting/banning Xim before, I think it was one of the black ops games. Maybe it never happened, maybe it turns out they aren't easily detectable, but it's come up before.