There is at least one event being held at Hyde Park as AEG are doing a signup for info for that much like the Jovi date:

http://www.hydeparkevent.com/

As far as the Olympic Stadium goes, I think they might have started removing the retractable upper tier seating (or they were at least going to) so being too large a capacity will not be a concern as they could easily just sell tickets based on the lower tier and standing.

It would be great to happen and would be a really special gig in amongst a good few special gigs on this tour, and dont underestimate how many casuals would go to this gig because of its location, and BJ would have enough hits to convince them to turn up.

I still expect them to be at Hyde Park, probably the first day of a festival resembling HRC but under a different name (Absolute perhaps?) but it's good seeing the Olympic Stadium coming down the rails as an outside bet.