Going to offer my opinion on some more "controversial" ideas because I feel like it.
I didn't love the Belgian Format. There isn't really anything wrong with it, I just think it takes very long and starts to feel like a slog after a certain point. It's not a dealbreaker though, and I'd sign up if it returned. Assuming we can't afford 8 teams, I think I'd rather just take the top 4 teams from the starting 6 and make that the playoffs. Yes, that's a lot of teams to pull, but I think it's fine. It gets more games played and will probably make the final weeks seem less hopeless for the bottom teams, as mathematical elimination becomes more difficult. I don't really mind the #1 Seed Bye, but I know a lot of players dislike it so it might be a good thing that this method kills that as well.
Regarding included tiers, I think I'd keep it the same as last year. The five OU tiers were competently filled out and I think it was really cool that up-and-coming players got to start in OU and show off. A lot of times these players get slotted into lower tiers or just go undrafted, so I think it is very good that more players got to participate, develop, have fun, and establish themselves. No matter what format we do, I think we should keep at least 4 OU slots. The best-of-five slot seemed popular too, so keep it. The lower tier slots were fine as well. If anything had to go, I'd probably cut PU, as I think it has the smallest community and isn't a very well-liked metagame right now. I think I'd rather see something like Tradebacks or Stadium there, as I think they are frankly more deserving of development at this point and are arguably just more interesting metagames. I'd like to see if anyone else shares this opinion, but I think PU will probably prevail because it's simply the largest of the three at the end of the day, which is a perfectly valid reason to keep it. A second Random Battles slot is also potentially justifiable. Speaking of which, keep Random Battles. I still don't know if it's the best meta for a PL, but I think it is essential to rope in that part of the RBY Community. Random Battles players comprise a huge portion of our community and they get ignored all the time. This format is great for introducing these players to each other and unifying the three subsets of the RBY Community, OU players, LT players, and Rands players.
This is self-interested, but please do not make LTs best-of-five. Keep best-of-five to Random Battles and the one OU slot. I think saying teambuilding for these tiers is easy is a gross overstatement. Teambuilding is as effortful in LTs (at least UU and NU) as it is in OU, in my opinion. Speaking from NU, which I've been playing most right now, there are a lot of moving parts to consider and there really isn't a streamlined build yet. These sets also just risk taking forever. I'm not a clicker and often take a minute or two between games, so a five-game set can easily take two hours for me (I know from experience in the RBY NU Invitational). I really just do not feel like committing this time and scheduling will become a pain. I love RBY LTs and think more games are better, but that is just a lot of time. And forget it if one player is going for partial-trapping spam. Individual games with that are liable to take 30 minutes or more alone.
I'm mixed on the RBY OU Blitz slot. On one hand, I think the tier has some enthusiastic proponents, so you might muster some additional signups that otherwise wouldn't have showed. It's also a way to spice up the 5 OU slots (which Tradebacks, Stadium, or Triple Threat would too!). On the other hand, I just don't really like the metagame. I'm not going to pretend it's not skillful, but it is a different set of skills at play. I think standard OU is more reflective of the skills that players are looking to cultivate when they play in a tournament, and there really isn't a sizable "Blitz Community" that we'd be catering to with its inclusion.
tl;dr We should include RBY STABmons in RBYPL.