It should come as no surprise that I am obviously in favour of adding GSC UU to this tour, there's been quite a bit of demand for it as Lily has noted, and its an absolutely beautiful UU gen that has a strong balanced nature to it and consistently offers high quality games when between people of similar skill levels.
The notion that it is some stall infested tier where all games go to 500 turns is obviously a completely false stereotype based on the occasional long games seen in tours like UUPL, where this situation could easily occur in other tiers like SM UU if both players brought stall anyway lol. GSC UU has definitely been becoming more offensive in recent times, and you'll see a lot of shorter games featuring more offensive teams orientated around stuff like Gyarados + Spikes, SD Scyther Pass with recipients like Nidoq/Bull, SD Victreebel etc, and a general move to more offensively inclined defensive cores with Pokemon like Mr.Mime (especially RestTalk in this context) rising up to be one of the top Pokemon in the tier.
Concerns about the mechanics like hs brought up are typically just brought on from a place of either inexperience in the tier or judgements based on selectively choosing the longer games really. Rest + Sleep Talk among other things definitely creates a more bulky orientated metagame, but progress is still easily forced between stuff like Spikes and Thief, as well as the fact that the Pokemon that typically are reliant on rest talk cycling are usually offering opportunities for Pokemon like Nidoqueen / Gyarados etc to eventually break through them with Spikes + chip, potential doubles, and the obvious chances to fish for crits that playing passively around them provide, as well as the passivity creating opportunities for other stuff such as a Scyther pass, Granbull / Kabu set up etc.
On a personal level while it might seem like i'm obviously biased as one of the most "GSC obsessed" people, this is actually pretty much a nerf for team UK if this happens, As I am already in the position of one of the only adv/dpp players on our team, and would create a further gap if i had to fill GSC.
Can regions actually fill a GSC Slot?
Based on like UUPL and some UUFPL players too, as well as known GSC UU players, you could tentatively come up with a list like this for most of the expected regions.
- UK: Estarossa
- US NE: ?
- US West: Siatam
- US Midwest: Kaori, Mr.378
- US South: HSA, d0nut, Lord Thorx
- Latin America: Raahel
- Brazil: LpZ , Highways, Hyogafodex
- France: Zokuru
- Germany: leru , vani
- Europe: Reece, cherryb0ng
- India + RoW: devin
- Canada: ? losing 467 and solo definitely stings on this front unfortunately
While i'd agree that certain regions are a bit more stacked than others on this front, for most part GSC is actually going to be relatively easy to field for most teams. Dependent on interest from more busy parties you've always got options like pirate for RoW too. US Northeast struggles but is already an incredibly strong team in general, and still has people capable of passing teams (such as Accel) to whoever gets slotted in there.
On the notion of GSC being hard to slot someone into?
I don't really agree with this notion necessarily, I'd argue that while there's going to certainly be advantages to more experienced players as in any tier, GSC UU is actually noticeably easier to pick up for an experienced player being passed teams than another generation might be, especially gens like ADV with the lack of team preview, or gens like BW which can be really unforgiving to small mistakes due to the highly offensive and fast paced nature of the tier. Lack of team preview isn't the biggest deal in the end due to rather limited pool of mons + more obvious structures, and its not very difficult to really learn the sort of threats you really need to keep an eye on and know which defensive responses you absolutely shouldn't be throwing out for no reason like Omastar.
In my mind any solid balance player in later gens should have a lot less difficulty picking up GSC to a high enough level to compete in UUWC than quite a few of the other generations of UU really, and as seen in tours like UUFPL, mains of other GSC tiers like Vani have been more than capable of picking up GSC uu and playiyng at a strong level due to GSC skills beeing highly transferrable, meaning teams like US NE can easily field a player who is strong at GSC OU as long as they have someone able to supply teams.
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All in all i'm definitely in favour of GSC's inclusion and think its definitely something that should be considered here. In terms of whatever 10th slot is added i'm relatively ambivalent and would be perfectly happy with RBY inclusion if RBY UU players believe it to be feasible this year, but favour a 4th SS slot, it would definitely have some beneffits in terms of accessibility and opportunities for newer players to make a name for themselves, while providing a side benefit of some further metagame developmeent in a fresher post sciz/mew environment.