They really did create a new entry hazard and only let it exist for a single generation since it was tied to g-max. Definitely think it would be cool if Copperajah got it as a signature, or if it was added to move tutors in the DLC, cause it seems like a massive missed opportunity for a new mechanic like that to only exist for the duration of a mechanic people only used in doubles anyway (though they've certainly done worse with dragon/fairy still being only on a mega evolution)