Concerning the SDK issue:
-What are the main reasons Ubisoft is not willing to release the full SDK?

-According to sources, Arkane Studios had already made the SDK but Ubisoft denied releasing it, why?

-Does Ubisoft have any interest keeping their game communities alive?

The find utility will help sometimes...
I guessed an answer yet before
Aside this, I think UBI gave us an idea about its knowledge in software development here...

Just wait, the next game will be sold cracked already (thanks UBI, why bother with emule or torrent?).

For what concerning the game communities, UBI complained about the lack of profits in the PC game market, then, if you wanna play UBI in next future, buy yourself a PS3 or XBOX and shut up...