This is just the info I read in today's FT; with regards to slots, I think the relevant authorities (whoever they are) would demand both parties give up a number of random slots at the relevant bases of LX and BA....not just the ones used for flights to/from LHR and ZRH, but a number of other slots too....this is probably why BA is worried.
Regarding LX's longhaul fleet....too large a fleet might mean Swiss is able to undercut competitors through capacity dumping....and one might wonder where all the money for all these large aircraft is coming from, and whether it is necessary. Whether BA has any business in deciding how many longhaul a/c LX should have is questionable, but then again, BA has to protect it's own position, and that might mean investigating management practises of competing airlines (just a guess, as I have no idea).
Furthermore, LX has been suffering a number of operational problems recently...whether this has any effect on current negotiations to join OW is debatable, although other OW carriers have seemed quite willing to reach agreement with LX thusfar.
An interesting development, although I'd be surprised if something couldn't be worked out; I am surprised by the apparent rejection of LX into Star (or at least rejection of a 'proposal') by LH....again on the grounds of the ZRH hub, and LX's supposed 'overcapacity'.