We know from the backstory in X that the Samaarians apparently arrived in that world from another plane of existance, so interdimensional travel or something of the sort does canoncially exist in that universe, as opposed to the obviously not canon Land of Challenge stuff. And since we never actually learn what exactly Elma is - as in, what species - I was thinking that perhaps she could even originate from another dimension entirely, with the events of 3 then potentially also being about how she got to Earth to begin with.
On the other hand though, this sort of dimension-hopping from the Samaarians could also serve as a way to get her (and other X characters) to wherever exactly 3 takes place
after the events of X. Truth to be told, I'd still prefer a X remaster or sequel over this kind of scenario, but it'd be better than the "it's just a follow-up to 1 and 2
" approach that currently seems likely.