I presume most of us will agree that such a change of alliance will not happen over night and that ties in alliances - in oneworld especially - have losened.
But there seems to be little facts agreed upon as to the costs of such an alliance-hopping and very different opinions on the value of Air Berlin to oneworld and vice-versa.
In spite of the short-term denial from AB Coo Gregorevich (ex KLM/Martinair) however, the possibility does seem to exist: AF/KL is publicly pushing for such an alliance change and Etihad has it's own reasons to be biased against oneworld (and whoever pays for the party chooses the music).
Certainly AB couldn't financially afford a change, certainly Etihad can't buy majority shares in EU-airlines, but a sceanario like EY buying a large minority share in AZ, then trading in both their shares in AB and AZ for a smaller share in bigger AF/KL and by increasing this share enabling AF/KL to buy deeper into AB and AZ have already been discussed elsewhere.
To me it seems that AB is currently making more than desperate cuts and trying to aquire capital on the free market even at disastrous terms just in order to avoid to use up the remainder of their credit from Etihad or even having to ask for more. The public criticism of AB Ceo Mehdorn by Etihad fits into this scenario and could indicate AB is struggling for their last bit of independence from Etihad and to stay in oneworld.
Admittedly, recommending the lounge of a member of a rival alliance to all your status customers (and not only AF/KL codeshare passengers) in Berlin is certainly unprecedented, but probably BA isn't unhappy, as they will have had more AB customers in their Berlin lounge than their own customers (paid for, but taking up scarce seats).

Just as many of you I am disappointed, that AB still has not taken proper care of fair and correct advantages for oneworld status members (entering number in reservation, free seat selection, seat blocking, entry to pseudo-lounges...), shows little effort to fly to oneworld hubs and offers very poor mileage credit for oneworld airline's flights (at least Etihad treated equally bad) to their own customers.
But equally I see too little effort from oneworld partners to connect to Air Berlin flights: S7 was AB-partner already before either's oneworld entry, CX goes everything alone, QF is lately obsessed with fighting their alliance partners, IB at least now has entered into a few codeshare-flights. But where are LAN, RJ or JAL? And where is BA who brought AB into oneworld? Are they not interested to free up slots in LHR for their partner to feed their own longhaul instead of now flying to DUB parallel to their own codeshare partner?
Only with AA and AY seem to be working successfully with AB to the benefit of both sides and indeed the number of English-speaking customers on AB flights has increased to my impression.
Agreed: waiting for your hub to get finished is a good reasons for partners not to fly there. But it doesn't look like this will change once the airport is opened. Yields and potential customers within 2h driving distance might be slightly lower than Frankfurt (if this were the main criteria everyone would fly to DUS), but having an extensive onward feeder network must be of some value.
It is certainly understandable that BA have their hands full with integrating BMI (having to put up with 3 terminals in LHR again is certainly a massive setback) and IAG with IB and that Willie Walsh's "shopping list" issued last year (including TP, AY and AB) is no longer of interest. Especially after BA burned enough money in Germany (ironically DBA is now part of AB) and France it is understandable they allowed Etihad to step in as AB begun to struggle.
It certainly didn't help the cause that BA then favoured Qatar instead of EY into oneworld. EY in my view would have been a better match with a hub where people might want to fly to and established links to oneworld members and partners (AB, EI, UL, MH, ...). Etihad's muscle flexing (AF/KL; Virgin Australia) in advance of negotiations certainly had negative effects, but Qatar did the same towards Airbus (A346), Boeing (B748F) and it's Cargolux-partners. And given BAs track record on finding partners (KL, LX, IT, AB...) I had hoped oneworld would opt for EY.

So, Oneworld doesn't offer enough for a member struggling to remain oneworld member against it's biggest shareholder.

But what can Air Berlin offer to Oneworld?
I still believe that it is a big mistake to believe that you can serve the biggest market in Europe (and from oneworld view this should include Poland, Chzekia, Slowakia, Hungary, Austria, Switzerland, Benelux and Germany, all connected via AB) from the outside. No sane person flying within Central Europe will connect via LHR. It is the same error as to believe you can serve the market in China and tie frequent customers there only via Hong Kong or the African continent via Comair. In fact, KL always benefitted greatly from the fact, that due to slot restrictions BA even have moreless deserted their own backyard in the UK, which could also be connected to Central, Eastern and Southern Europa via AB.
When BA invited AB into oneworld I had hoped the lessons from the failed attempts with KL and LX had been learnt (after all AB was the last potential partner still available), but I am no longer convinced they have.
I have read some disappointed experiences from oneworld customers here. I guess most are due to the poor treatment of status advantages by AB. But comparing my many flights within Europe (only comparing economy, which is sufficient on shorthaul - but I agree not satisfying after a longhaul connection) AB, in spite of recent cuttings in their network and their service, still is one of the best carriers in Europe (overshadowed by TK, on par with BA,LH, TP, LX and OS, slightly better than KL and AY, noticeably better than AF,SK and 4U, miles ahead of IB, UX and FR).

So the question really is: will AB finally prove to oneworld, that they are worth more assistance from oneworld members to help them stay in the alliance against the will of their biggest shareholder and probably bring their partners Meridiana and Pegasus into the alliance, further closing existing oneworld gaps in Italy and Turkey. By the way: Hainan is also a partner of AB.