Of course, any PR plans would have rather broke this information on their terms but that is the risk of making others aware before you have the opportunity to go public. I'm sure the club will still present this professionally in their own time, and we shouldn't have long to wait.
The club have worked closely with OCC and CDC to help smooth the planning application process. One of the key points is having a stadium perfectly placed for all public transport routes and helping to keep cars from the city centre. Alongside plans to make the stadium ecologically sustainable will help get the green vote.
I'm not aware of any plans for the stadium to be used for other sports, but wouldn't entirely rule this out. I'd certainly think that we'd put ourselves forward as hosts to England's women's games, or the u21's etc. As for concerts, I'd certainly hope that happens from a personal perspective but it may depend on how close the actual ground is to housing. I suspect that noise limitations may be a barrier.
As for the wider complex, then the hope will be for it to be used daily in order to maximise income. I don't know how much revenue is generated around stadium MK, but there will be a similar plan to make it a community hub outside of matchdays.
Finally, the training ground was taken on with a lease arrangement where the club committed to maintain it for the wider community throughout the duration of the lease. So there won't be any immediate plans to close up shop, and it's probably more practical to keep the training facilities separate to the ground.