KLM/AF obviously assume that Brexit won't affect ownership rules ... we will see.
I can't see many passengers wishing to transfer between VS & KL or AF at LHR as you can fly non-stop to CDG & AMS from just about any city with a route to LHR (although I haven't done a detailed check). It wouldn't really be worth any of the airlines changing terminals.
I said at the time that DL acquired 49% of VS that they really needed a 51% share - SQ was unable to influence things with their 49% share - but of course that it was not permissible and that AF/KLM should acquire a 2% share. Well they have gone further than that. However DL seems to be in control with a minority stake. VS is certainly in a better shape now than when DL acquired SQ's share, this year's loss nothwithstanding.
RB has often said that he gets bored with businesses and likes to move on. VS has been an exception, but maybe he no longer feels that it is his airline. Now that he lives on an ocean islands and seems more interested in spaceflight maybe that is what has happened. Either that or his empire is short of money.