As wiggy says, BA’s strategy is becoming clearer. The preference for cadets seems to be driven by the notion that they are “cheaper”.
However, and I must stress that it’s only my personal opinion, I think there will be opportunities for DEPs in 2018. The reason is that the last of the FPP graduates will be joining the ranks fairly soon, but the new cadetship will not start yielding line-ready pilots until (possibly) summer / autumn of 2019 at the earliest. And I really doubt L3’s whitetail candidates will be able to exclusively satisfy BA’s demand for pilots next year without the training department going into overdrive.