I was hesitant on commenting here because I know I'm just going to be regurgitating common sentiments without providing much of anything original but for a 10 slot tournament I think 3 current gen (SS) and one of each other gen going all the way down to 1 is quite easy and makes enough sense. The main three questions I see different answers to are as followed:
1) Is RBY ready to show its face in the tournament scene again? It was met with a lot of negative feedback in the previous Snake tournament for completely justified reasons. Although plenty of metagame development has been made in the tier, as far as I'm aware no actual tiering action in regards to the biggest issues with the tier, revolving around Charizard and Fire Spin, and Poliwhirl and Sleep-inducement. Regardless of which aspects have action taken upon them, I personally thing RBY is simply too young to see itself in a tournament that we would want to have high standards for.
2) Will GSC even receive enough signups? Obviously a far smaller issue, and not much of an issue in the first place, but it does have some weight to it. GSC NU "mains" are far and few between, with the CEO of the tier on a tentative break. Big names like Siatam, Earthworm, and Estarossa obviously would make for some great games, but are there enough players so every team can have a competent player in an admittedly complex generation / tier? It wouldn't make sense to include a NASCAR race in which a majority of the competitors don't even have a driver's license...
3) In light of potentially dropping at least one of RBY and GSC, would there even be a suitable replacement? I think the answer to this is just no, although that does not mean RBY or GSC should be kept simply because there's nothing better. The most feasible solution is a best of 3, either with the 3 most modern generations, or one similar to the Homefield tournament format, where game 1 is SS, and the proceeding loser picks a generation of their choice. The first bo3 format is the most consistent, although the amount of prepwork needed for one slot makes it less ideal. The homefield concept, while probably more fun and versatile, makes prepping pretty much impossible unless played over the course of an entire week or players lock the tiers at the beginning of the week or for the entire tournament (I prefer a weekly basis). The discussion of BDSP or a petmod NU are not viable for the standards of the tournament I mentioned earlier. No disrespect to the members who run the tier and made it as good as it possibly can be, but BDSP is simply just not good. The usage stats are incredibly warped and inaccurate due to the disappointingly low game counts on the ladder, which really shows how willing people are to play it. Beyond the technical aspects for why its far from an ideal option, mechanically its just not fun; modern mechanics on Pokemon is nice, but they're completely gutted from their typical movepools and some item choices. Other petmods like Aawin and I's MutantMons have no place here, although I will be hosting a tournament for it soon :)
I'm curious to see the different answers to these questions because they obviously are all subjective, so the best course of action moving forward is to consider what we want Snake to be (I'd imagine featuring all generations is the common goal) and also abide by majority rules.