Spot on with my thoughts too. Im almost certain we will see a buff/nerf coming with the final update too. With all the typing events I feel like there will be a powerhouse or two from almost all the types now vs the "big 7" and nothing else.
I'm not sure about a buff/nerf coming with the update, at least not in the terms of another CP recalculation or move changes/updates. I think just changing Super and Not very effective relative to STAB would shake things up plenty. Also, with the impending TMs to change moves, we'll already see all-new move-sets; think of a Pokemon with a legacy move (either quick or charge), and re-rolling the other one, resulting in one legacy move-set and one newer move (I don't think re-rolls will let you get legacy moves). That also potentially means even more "dual-legacy" type move-sets if they ever change move-sets again, which could make things really interesting long-term as far as unique move-sets are concerned.
I do think that there will be a few "meta" or "powerhouses" of each type.
For water, there's the obvious Vaporeon, as well as Gyarados, Lapras, and Feraligatr also having decent CP and potential uses.
For fire there's Flareon and Arcanine who are pretty decent, especially with the newer fire moves, and Charizard and Typhlosion aren't bad either.
For grass, Exeggutor and Venusaur seem to be the only really viable grass-type mons, unless things really change somehow.
For rock/ground there's Tyranitar, Rhydon, Golem, Omastar, and Donphan.
Psychic has Espeon, Alakazam, and Exeggutor, as well as Slowbro and Slowking.
Normal has Snorlax and Blissey of course.
Bug has Heracross, Scizor, and Pinsir.
Electric has Jolteon and Ampharos.
Fighting has Machamp, Heracross, and Poliwrath.
Dragon has Dragonite and potentially Kingdra, especially if they change CP up.
Dark has Tyranitar, Houndoom, and Umbreon, especially if they change CP up again.
Steel has Scizor and Steelix.
I think all of the above guys could have their uses/roles.