As far as I remember, MOL has repeatedly announced that FR will leave BER once it replaces SXF. The fees at BER will increase dramatically, not only compared to cheapish SXF, but also to rather pricey TXL. When the fees were published a while ago, there was almost some sort of mutiny among German airlines.
AB currently serve BKK from TXL, but they will have much more expansion space at BBI.
AB are almost bancrupt. They will be happy if they survive next winter with almost all their capital burned (as you will have noticed, their CEO stepped down the other week thanks to the disastrous performance of the airline he sort of founded). Even if they do survive, they do not have the fleet to set up a proper longhaul hub. Besides that, if BER is the only place other than HEL and PRG to offer these advantages, oneworld already has Finnair and HEL - do you expect BA/IB to dump them like a hot potato?
In the end, BER is just another new airport in an already crowded European market that lacks a strong home carrier that could turn it into something bigger.