It's fairly obvious that LMP1 is on BMWs mind and as we say in German, "Aufgeschoben ist nicht aufgehoben", which roughly translates to "Just because you postpone something does not mean it's not going to happen"
I think the GTE effort is a trial for BMW in many ways, if they feel they´re getting their money's worth for being part of the WEC then they'll join LMP1 as soon as the rules fit the technology they want to bring.