Just my two cents in the matter.
Laddering this gen has been really, really fun. Probably the most fun Ive had with a new gen outside of early days mega chaos of XY. In addition, I dont particularly have too many problems with Tera, but thats just my playstyle. I play conservatively, and oftentimes keep Tera in the back pocket to such a degree I find myself winning the game without Tera-ing 3/4 times.
As others have echoed, I dont think a restriction is going to solve much of anything. We might see differently in SPL or whatever major tourney sees high level SV play first, but for now, the most popular tera types have, for the most part, been discovered. A "Tera type at team preview" doesnt really solve much apart from examples like the Tera fighting Garganacl example posted before in this thread, people are, for the most part, in tune to the possibilities your Tera types can be when they load in. All preview tera really does is reduce the pool from maybe 2-3 types to 1 per mon. I dont think thats a significant change at all.
I think the most major problem in the tier right now is how bad balance seems to be. Semi-stall and stall have their place, Offense and HO have their place, but mons like Annihilape, Roaring Moon, Gholdengo, Great Tusk, Dragonite, etc shit over Balance pretty hard. Teamstyles that were niche in previous generations, like Webs or Screens, are just really good this gen with the high power level of the tier, and Tera is excacerbating the issue. I'm not saying that Webs/Screens needs to go back in the shadows or relegated to lower tiers, but this tipping of the scales, while personally fun for me, seems like it will eventually lead to a bad state of the meta. Im personally very interested in viewing high level tournament replays of this meta, because I dont see any way that its not going to confirm what I suspect: HO and Stall are ruling the tier, HO because the playstyle takes the most advantage of Tera, and Stall because its oftentimes the only way of defensively withstanding the offensive juggernaut that is a boosted Tera threat. While the knee jerk reaction is to call this favoring bulkier teams or saying that not every meta has to be the same, I just feel like this situation makes the meta tend towards rewarding matchup fishing. Sure, Tera is fun and its really fun laddering with it and playing with it, but the real question should be is it good for the health of the tier? Does it lead to a consistent metagame? Laddering with it is fine, because hey, if you run into a Tera that counters your whole team, thats fine, load up another game. Playing Bo1 tourneys with Tera? I imagine it'll just lead to players trying to out-Tera and out offense one another, and a lot of games lost at team preview, and that, in my view, is just not at all consistent or competitive.
As much as I enjoy the mechanic, I dont see it staying, and Im okay with that, because at the end of the day, we should be trying to achieve the most competitive metagame. Im sure there will be an OM that satisfies my Tera urge, and thats why I think it should be suspect tested at the very least.
Thank you all for reading!