I think most of the oneWorld partners have their focus on their own backyards rather than pushing for more integration..
As MarkD says, there are still quite a number of european destinations where EI don't overlap BA. (Scandinavia anyone?)
Why would EI leave oneWorld? Really?
Why when by the time the bilateral goes, AA will feed into DUB to feed into EI's expanding european network, instead of having to look for more slots into and out of LHR..
Why when EI will codeshare westbound with BA out of LHR?
BKK: unlikely
DXB: possible, as is the codeshare with EK
CPT: watch this space...