It will come as little surprise to anyone that Branson hasn't actually advanced a formal proposal to take over Concorde, as Patricia Hewitt noted this morning in her announcement. There is an incredible amount of publicity value in Virgin's actions but very little substance to show.
It also cannot be a foregone conclusion that Virgin taking over Concorde services is in the public interest. What other services is Virgin going to cancel - reducing competition for the subsonic masses - to create the runway slots needed for Concorde flights?
One cannot help but think that it would be highly amusing for BA to say "yes" to Branson's scheme. Branson would probably need a change of underwear on the spot at the prospect of having to deliver on his promises or face ridicule. It's almost worth persuading BA to agree to his demands just for the sake of watching his face when he hears the news.