I really cant see BA putting up with sharing 'their' terminal with a major competitors budget arm!! Believe it when I see it...
It is no longer BA's terminal the lease is now up. Rumor has it that nouthing is signed with BMI or BMI baby yet and if anything happens then it will not be untill summer.
One problem for there long haul could be the fact T3 only has 2 stands that will fit A330's on all the others will only fit up to 767's on.