ArchedThunder
Banned
I could see machine type happening, even if it's not as much a 'duh!' move as the fairy type. Pokemon like steelix, aggron, escavilier etc would stay put, representing natural steel and any mechanical Pokemon would get the new type. Off the top of my head, I can't think of too many existing mons that would get retyped; magnezone and klinklang jump out but that's about it. They would need to introduce a good amount of new lines in that case. Say gen VII has a steampunk theme (what goes hand-in-hand with steampunk? Fucking Britain! Get on it Game Freak!!) that'd give them ample opportunity to fill out the dex with machine-types. And it would make it a nice round 18 total.
For strengths and weaknesses I'm thinking:
Resists: fairy, electric, psychic, steel (fairies don't do well with machinery, electric powers them and psychic doesn't affect their computer minds)
Weak to: water, ice, bug (water for obvious reasons, ice freezes their circuits and definitely needs a buff, the classic 'computer bug'
Super effective: fairy, electric, fighting (fighting I figure b/c they're able to calculate their moves easily)
Not effective: water, ice
Pokemon that could be Machine type.
Magnemite +Electric
Magneton +Electric
Beldum +Psychic
Metang +Psychic
Metagross +Psychic
Magenzone +Electric
Klink +Steel
Klang +Steel
Klinkklang +Steel
Golett +Ghost
Golurk +Ghost
Genesect +Bug
The Porygons could also be thrown in if they felt like it.
There is definitely enough there, but honestly if we got a new type I'd kinda prefer it be Sound type.