Given what I've seen, I'd expect the following in 2.3:
1. New physics. The game will probably have the physics tweaked to be further in line with the 2D classic Sonic games. Higher jump heights, heavier gravity, and slope physics while walking instead of just while rolling I think will definitely be in 2.3. I know that loop-de-loops and such are controversial, mainly due to the high amount of sprites needed to make them work, but regardless I think there's still a good chance for them to be in 2.3, since Ring Racers added a lot of new mechanics compared to SRB2Kart despite worries that the high amount of sprites required to make them work would take too much effort. While Kart Krew is not Sonic Team Jr., both teams share a lot of devs, so I think the comparison to Ring Racers is relevant.
2. New character movesets and sprites. The new movesets and sprites IIRC are coming in 2.2.14, but I think they're still worth mentioning when it comes to 2.3. Amy will be completely reworked so that she resembles herself from XMomentum more, and Fang might be changed to be a little less clunky (no loss of speed from dropping tail bounce in the air, the ability to shoot while moving or in the air perhaps?) and Metal Sonic might get nerfed a bit, as I remember people complaining about dashmode and hover being broken. Sonic will probably lose the Thok. I personally wouldn't be too happy about this, but it's not something that's a dealbreaker or anything (I just like being able to "unga bunga" fling myself through levels.) I'm not sure if the Scrunk will end up being the final replacement, but I think it is possible that it makes the cut.
3. Completely revamped existing levels. GFZ, THZ, DSZ, ACZ, and ERZ will probably receive the most extensive overhauls, while CEZ, RV1, and BCZ will probably see less extensive revamps, but still be retrofitted with more advanced level design to compliment the new physics and enhanced mapmaking tools.
4. New acts for the existing zones. RVZ2, RVZ3, and ERZ3 will probably end up appearing. I'm aware that ERZ3 was cut because that would make for too many bosses in the endgame, but I think it still has a shot of making it in for 2.3 to accompany the complete overhaul of ERZ1 and 2.
5. The completely new levels and revamped old levels will be enhanced with more colour and detail.
I saw a discussion post from around 2019 on this exact topic, and I saw a few members of Sonic Team Jr. agree that the game could use some more varied colour palettes. I think it's very likely that the levels that receive the most changes to colours are THZ, DSZ, ERZ, and BCZ, due to the fact that (IMO) they suffer from this problem the most. It could be argued that CEZ also suffers from being too dark, but I think in its case it helps it more than it harms it. As well, I know that Sonic 3 & Knuckles inspired level transitions are something planned for the game, and I think it's likely they could make it in with the campaign overhaul.
6. Several bonus levels will be cut. I think PTZ, TLZ, AGZ, and ATZ are probably going to be cut in 2.3. I believe PTZ (and perhaps Mario Mode as a whole) has a good chance of getting cut because of Nintendo's aggressive copyright claiming of fanworks. Even harmless stuff, like Nintendo addons for the Garry's Mod workshop don't escape Nintendo's wrath. I think Sonic Team Jr. would rather cut PTZ and Mario Mode from the base game than put SRB2 in danger of getting taken down. TLZ could get cut for being generally unpopular, as it's not all that fun to play IMO. AGZ and ATZ could get cut for similar reasons, but also for their connection to a certain someone who is no longer welcome in the SRB2 community.
7. New menus. While the old-school Doom menus are charming, they're also clunky and visually unappealing. I expect the showcased menu overhaul to make it into 2.3.
8. Add-on unloading. Having to turn the game off to unload addons can be pretty annoying, so having the ability to manually unload them in-game would be a much appreciated QOL feature.
9. Software palettes in OpenGL. I personally use OpenGL and prefer it overall to Software rendering, but I definitely think that Software has much more appealing colours. I would really appreciate a way to see those colours while using OpenGL.
10. General polish and enhanced visuals. I think a lot of the game even aside from what I've already mentioned has a good chance of having more polish and visual flair added to it, like the new emblems that have been showcased.
11. A release date of sometime in mid 2025. Speculating on release dates is silly, and for a volunteer fan project like this, perhaps even a little entitled, but regardless I think it's totally possible for 2.3 to come out somewhat soon. If it does end up taking longer, it's no big deal. I already like SRB2 a whole lot the way it is currently, so I'll be perfectly content waiting for as long as it'll take for 2.3 to come out.
12. A great game. I know that's a lot of pressure to put on Sonic Team Jr., but I genuinely think SRB2 2.3 will be a fantastic game. I'm not kidding when I say that SRB2 2.2 is my favorite Sonic game of all time. In the Discord I posted my own personal tier list ranking of Sonic games by how much I liked them, and SRB2 was in top tier along with Sonic Mania and Sonic 3 & Knuckles. I have faith in Sonic Team Jr. to make a game that'll blow me away completely.
So, this is my first post on this forum. I've been lurking for about a year or so, and I've finally built up the courage to engage with the community a bit more. I hope this follows all the rules and ettiquette required for posting here, as while I have read the rules, I'm paranoid that I might have accidentally missed something, or I might have said something the wrong way. So, yeah. Hello!