You still can through Xim I think. As a matter of fact there are console players run MnK through Xim

No one on console would use mnk. They barely use mnk on pc...

I don't know about Sony but Microsoft are a little apprehensive about opening M&KB use for all games, currently there are a few that are officially supported but MS are still working on various hardware aspects as well as making sure M&KB on Console won't cost them PC software sales somewhere down the line. Even then it has to be agreed by the developers of any particular game, as well as coded in. For Destiny the coding wouldn't take much as its already there for PC (and consoles are basically focused-function PCs anyway) but would Bungie allow it knowing already there is a big divide between controller and M&KB users? Its not just Destiny of course, this conversation has raged for years. Some are more comfortable with one and others with the other, but it can't be denied a skilled M&KB user has advantages over even a high skilled pad user. I'm a controller peasant myself, I've played Destiny against M&KB users on PC amd I can hold my own mostly, but I can tell when I've been out-gunned by a mouse. I don't cry about it, thats the deal but I can see how it would get frustrating if M&KB was suddenly officially supported and half the console population started using it. Bungie would lose console players, I can't see them risking that.

No even if you want to use it for pve there is no stoping someone else to do in in PvP so no