This would be like Nintendo saying "200 doubles is our standard metagame" during the Advance generation. It's certainly an interesting decision. This could turn out to be a sweet metagame, I really loved 200 when I started playing Advance. No move tutors, almost no Stealth Rock (although doubles teams don't usually run this), hardly any walls, it's too bad that they limited themselves to like 40 viable pokemon from the start though.
We might even see teams using Sandstorm (the move) like doubles teams used to use Rain Dance. No Sand Stream pokemon exist in Isshu, but Doryuuzu does. And it gets EQ and Rock Slide, effective moves in doubles. There also isn't much incentive to use any other weather, since only two pokemon get Swift Swim in Isshu (one through DW) and Sun has never really been great. This whole metagame is going to be Doryuuzu + Roobushin.
We might even see teams using Sandstorm (the move) like doubles teams used to use Rain Dance. No Sand Stream pokemon exist in Isshu, but Doryuuzu does. And it gets EQ and Rock Slide, effective moves in doubles. There also isn't much incentive to use any other weather, since only two pokemon get Swift Swim in Isshu (one through DW) and Sun has never really been great. This whole metagame is going to be Doryuuzu + Roobushin.