From what I saw of the sixmove tournament that happened, the focus of this metagame is more hyperoffensive than ever, because anyone can break through anything given the right opportunity. Priority would be useful- if only sweepers were less bulky.
In such a metagame, you'd need immediate counters, most prefarably mons which take the opponent's setup, and turns it in your favour. I can see Trick Room teams flourishing. I can see Gravity flourishing.
Quagsire@Leftovers
Unaware - Impish
Waterfall
Earthquake
Curse
Recover
Toxic/Yawn
Protect/Amnesia
Unaware wipes out any sweepers that can't kill it immediately. Forces out a grass type immediately if you're looking for one. Under Sand, this thing is horrible.
Ditto@Choice Scarf
Imposter
Transform
There is nothing more satisfying that wrecking someone else with their own boosted pokemon. Doesn't work on substitutes, so suggested with Extremespeed Dragonite or another priority user. Works for the same reason that ditto works in DW- this metagame is setup and hyperoffense everywhere.
Jirachi@Leftovers
Substitute
Calm Mind
Water Pulse
Psyshock
Energy Ball
Thunder
Wish
No idea what to place in the last slot. I suspect this jirachi may be a bit too slow for the metagame, but in theory it looks fairly pleasant- Energy ball outright kills walls, Psyshock kills Chansey, Thunder kills sweepers and Water pulse takes out the rest. Latias might be a counter, but it's not going to show up with dragonite everywhere.
Deoxys-D@Red Card
Recycle
Substitute
Recover
Cosmic Power/Agility
Taunt/Magic Coat
Spikes/Stealth Rock/Toxic/Thunder Wave/Trick Room/Gravity/Seismic toss
The reason for substitute is because Red Card hits THROUGH subs. You can bounce people when they break your sub. they are also forced to when you taunt them.
Another idea is Simple... uh... Swoobat, since it can now actually make use of it's movepool.
EDIT: Regarding Quagsire, I haven't actually used one myself, so opinion accepted and due noted. thanks for pointing it out. However, on another point, I don't think that even amnesia or a single curse will save it from an OHKO from ferrothorn or a leaf storm from anyone, tbh. Things like Draco meteor, maybe, but it's spdef is already ridiculous in sand- it doesn't seem to need amnesia. The only problem Quagsire would have is status in this case. Maybe Substitute, as ridiculous as it sounds? Does it get Refresh? If not, run a Sleep Talk set?
... Hey, thinking about Sleep Talk sets, they're going to be extremely effective since the chance of selecting rest goes down to 1/5. Things like Gyarados with Sleep Talk/Rest/Roar/Dragon Tail/Thunder Wave/Waterfall or something like that must be annoying.