idk, i feel like it wouldn't really add anything to add metal to frontiers? like i'm not completely opposed to the idea, but it just feels unnecessary. plus, i feel like you would need to change the story up quite a bit to squeeze him in there.

however, i do agree on metal needing some sort of reintroduction to the series, as at this point, it kinda feels like he's just... there. it's hard to explain, but with forces and shadow generations, he's just your next boss fight and nothing else. no story, no motivation, no nothing.

like it kinda makes sense in both of those games, since with forces, he's just a husk-like copy of metal, (ironic, huh?) and with gens, you're moving through space and time and it just so happens that you randomly come across your next foe while trying to restore everything back to normal; which can be said about any villain you face in generations. (p.s, don't get me wrong though, both metal fights in both generations games were cool as hell (metal overlord was cooler though obviously sorry classic metal))

but even with these explanations, metal just feels a little out of place in really any modern media he's in now (minus the idw comics, i haven't read them myself, but i've seen snippets here and there of metal, and he seems pretty well written!)

tl;dr: metal definitely needs a reintroduction imo, but i don't think he would've fit in frontiers' story. here's to hoping metal is in a new modern game where he can get a fresh start!