DL can't acquire any more of DL but there is no reason why AFKLM couldn't acquire the 51% & effectively outsource the management to DL (although there is still the question of whether that would be considered as EU control). Would a DL manager who is an EU citizen be OK?
As far as the ALPA scope acreement is concerned, I would imagine in any case that a VA pilot could only fly DL metal if a US citizen but a scope agreement forcing DL pilots to fly DL metal is enforecable although may need to work for the next contract to be signed. Similarly DL & VS can agree on broadly a 50/50 split or whatever on their joint venture between the UK & US - isn't that what KL & DL (and before them NW did between the NL & US)? BALPA could probabaly go to a UK court and argue that any scope argeement limiting the amount of non US flying VS could do was illegal - isn't that why EU airlines must be 51% owned by EU citizens?
(I'd like to know what BALPA would think if the Allied Pilots Association tried ti limit the size of BA's operations to that of AA.)