Koei Tecmo have almost no reason to get Team Ninja to do a DOA6, DLC sales are through the roof and there is also the fact that Team Ninja is busy on like 3-4 different projects on top of DOA5/DOAX3
There is no reason for DOA6 at the moment when DOA5LR is still being played, still looks fantastic compared to most FGs and is making profit for Koei-Tecmo.