Not much for Sora's part. I'm rather satisfied with what I can come up with about the floors (especially Monstro <3), though I think I'd like to explore DI more. Like, instead of just going through the KH1 story for it in five minutes or so, and thus show the bluntest contradiction in Namine's story, being that she's there at age 14 when she was supposed to have disappeared years ago, that we'd have gotten to explore more their homes, both Sora and Riku's, as well as Kairi's, and then see what they'd have came up with for Namine. I know family is unimportant but then again this is where Sora said his parents tried explaining Namine's disappearance to him, so. Meh.
The rest of it I suppose would be for RR, simply because it felt so empty. Personally, I think they'd have done a somewhat better job if they'd have kept Kairi (surprise surprise) as an active force on the DI world and have her accuse Riku. She'd have some more merit seeing how she's not only a PoH, but also one Riku half kidnapped, regardless of his views in the matter. Heck, that's how they described it in the Coded summaries, right? XD
Meh. Iono, mosrtly insight for Riku inside the worlds. Much like you said, seeing remnants of Sora would be nice, especially since for some worlds, Riku really was there, and it's not like he abandoned everything - Sora still was what drove him, for better or worse.