Ooh, lots of great ideas, and I love the idea that many of them may become a reality some day!
To accompany the playsets and standalones that already exist (or are strongly rumoured to), I'd love to see Frozone, Elizabeth Swan, Will Turner, Felix, Calhoun and Oogie Boogie. But I'm most exicted about the idea of different franchises getting figures. Soooo...
Lilo & Stitch Playset: Surfing! And possibly zipping around in those little hoverships they showed in the end credits. Lilo and Stitch would be definites, but Jumba and Pleakley would also be very welcome.
Merida Standalone: Archery, with a target-system mini game. Honestly, I'd love a Brave Playset, with Fergus and Elinor, but I think a Merida standalone is more likely.
Little Mermaid Playset: Underwater swimming would be awesome. Ariel and Ursula would be amazing figures. Not sure how Ariel would work in the toybox, but she could easily 'swim' through the air, like when a kid is holding a toy and miming swimming.
Aladdin Playset: Aladdin, Jasmine, Genie and Jafar, with parkour-style leaping over rooftops and carpet riding.
Lion King Playset: Simba and Scar, and I think I saw somebody mention Timon riding Pumbaa, which I think is a great idea.
Gravity Falls Playset: This one might be wishful thinking, but the idea of playing as Mabel makes my heart sing.
Peter Pan Playset: If this isn't part of Infinity 2, I'll eat my woolly Kermit hat. Peter and Hook would be obvious choices, but it'd be nice to see Wendy too. (Don't know how Tink would fit in, in terms of scale.)
Classic Disney Playset: Mickey, Minnie, Donald, Goofy, Daisy and Pluto. Again, I wouldn't be surprised if they turn up in Infinity 2.
Jessica Rabbit Standalone: Which basically comes down to the hubba-hubba factor. I'd love sashaying around the toy box as her!
Any Disney Afternoon Playset: Ducktales, Rescue Rangers, Darkwing Duck, Talespin, Bonkers, anything! Probably unlikely, but the Afternoon Vinylmation Series seems to sell well (and Scrooge's vault and number one dime are represented in the game), so maybe we'll get some standalones
Tarzan Standalone: The sliding rails from Infinity match the way Tarzan moves in the film, and he could have a swinging vine that works like a grappling hook.
Winnie The Pooh Playset: The Pooh Bear levels of Kingdom Hearts were just darling, and spending an afternoon in the Hundred Acre Wood trying to find hunny and playing mini puzzles could be an interesting alternative to the more adventure-based playsets.
Mulan Playset: Mulan and Shang, and potentially Shan Yu as well, with learning different kinds of combat, sword fighting, horse riding, and lots of action.
Maleficent Standalone: It could coincide with the release of the future Maleficent movie (although I'd definitely prefer the animated version of the character). In an ideal world, I'd love a playset with Aurora, Philip and Maleficent, with a big dragon battle at the end, but that seems unlikely. Maleficent on her own seems doable.
Princess And The Frog Playset: Tiana, Naveen and Facilier. I think they'd work best as human characters in the toy box and as frogs in the playset. The figures themselves could be Tiana and Naveen as humans with their frog counterparts posing at their feet, to indicate that you'll get to play as both.
Treasure Planet Playset: Yeeeeah, likely not something we'll ever see, although the movie could suit a playset so well. But it'd be cool to play as Jim and Silver.
Muppets Playset: I would die. I would just die. If nothing else, a Piggy standalone would leave me on cloud nine. Kermit would need to made as well, but Miss Piggy is obviously the centre of the universe.
God, I have to stop because I could go on forever and this is already long enough as it is. I know there are a lot of rumours about Rapunzel as a standalone, and while I'm sad she won't get a playset, I'd love to see her represented. Having Flynn with her would be awesome.
Honestly, the things I'd love to see the most are some more Disney Classics and more female characters. If Infinity does well, maybe we'll see Star Wars and Marvel in later versions, which would be beyond incredible!