I don´t think that has to do with fleet comunality.
It´s just the case that the fleet expansion of laudaair was far to aggressive.
The financial situation of laudaair in the last years was very poor to say the least, and it seems that it won´t get better this year. They have massive losts in the first moths of that year, and it looks really bad.
The 777 are extremely expensive, the laudaair contracts with boeing seem to be not really cost effective. The NG777 are the most expensive 777-200IGW´s on the market, due to "taylor-made" modification and outfitting (galleys etc.) and due to the very small ammount of aircraft ordered (2).
The unique "sale_and_lease_back-and-buy_back_and_sale_and_leasback" operations by the former CEO made the 767 fleet also a very expensive one. They have now the situation to have a very expensive to operate fleet, and dramatic losts.
Unfortunately Laudaair can´t cut personal costs, because Laudaair personal is avtually among the cheapest in europe. The will have to increase the income of their pilots, flight attendants etc., and they will have to decrease their workload. All that raises costs, and that in time of severe financial troubles.
The only chance they have is to get rid of unused, too expensive aircraft. But it will be very difficult to find a cutomer for their B777´s. Because their price is enormouse, and other airlines will get cheaper TripleSevens directly new from Boeing.
The new Management tries everything to avoid the delivery of the new additonal B777 to them, because in their actual situation a 1.7 billion austrian schilling aircraft (that they don´t need) is the last thing they want to pay for.
1.7billion ATS for a new B777 would raise their losts to a catastrophic level.