Hall effect switches have existed in keyboards for a long time [1].
I don't think there are many of them being produced nowadays though, but there's at least one new Chinese Hall effect keyboard that came out a few years ago [2].
Wooting also has a Hall effect switch [3].
You can't buy any keyboards with it yet but you can pre-order one at least [4].
Oh yes, I should have written "coming back". I have one from the 70s in my posession somewhere. I am more a clicky kind of guy (or at least proper tactile, not mx brown mush), but for linear switches I would love to be able to set the actuation point!