MCPE and windows 10 most likely will connect to each other when 0.12.1 releases. Win10, as of now, will run 0.12.0, but when it gets 0.12.1, they will be compatible. I'd say it'll release in around a couple weeks to 3 weeks.
^This, or very soon.
Right now the "Win10" version (I call it C++ MC for short) has some features that are in the 1.9 snapshots and not in a production Java version yet, like packed dirt paths in the villages. I think the latest xbox version also added these features, but the rest of the console and MCPE versions have not.
In the very near future we're going to see the consolidation of all these features to allow all the versions to play together. Then we'll most likely see features from "Java MC" added to the mix.
As someone mentioned above, LexManos said on a MineCon panel livestream that "Microsoft engineers are following me around asking questions" when he was asked about Win10 modding, so I don't really think we'll see a lot in that direction until the entire userbase can benefit.
