I would agree with Bex88 however, DEP has, historically, been a much lower training risk as the applicants are generally filtered at the interview/sim stage.
Hence I would suggest that non-type rated applicants can be fed through to fleets with a higher training capacity without a problem eg. A380 (if previous airbus experienced),747 and 787. There is also the A350 possibly coming and it would make sense to queue up future training assets to that fleet if the applicants have either SH Airbus or A330 experience.
My personal opinion is that the 777 has too much of an internal applicant backlog to allow DEP however no one can ever second guess what IAG/BA will do and it's their train set after all.