Never heard of these games
Kingdom Hearts Chi: Back Cover is the retelling of Kingdom Hearts Chi, but from the Foreteller's POV. (KHChi is a game that takes place years and years ago, around the Keyblade War era and has a fairy tale element to it, hence why it looks so friendly and cute.) The events in KHChi/Unchained/Back Cover seems to play a big part of what's going to happen in III.
Kingdom Hearts 0.2 was originally supposed to be part of III, but because they apparently had too much content in the game already, they decided to release this segment as its own separate episode. So essentially, you ARE getting KH3, just a snippet of it. (Think MGS V: Ground Zeroes) This is the game where you're playing as Aqua in the Realm of Darkness.
Can we just get KH III already
We're not getting that until 2017, at least. FFXV comes out next year, and I doubt Square Enix is going to drop two of their biggest titles in the same year. That's why we're getting 2.8, it should be able to hold us until 3 drops. Plus, I want them to take their time. This is going to be end of the first Saga of Kingdom Hearts and we're killing Xehanort, so I really want them to get it right. I can wait a bit longer.