I am yet to meet any 777 f/o trainees, but have heard they will be here soon.
So not sure really.
You will not be a threat to anyones eventual upgrade so do not see many problems with the job. The expat f/os I know here seam to get on fine and probably complain a lot less than other airlines I have worked at.
As a short term job prospect, I think it could be worthwhile depending on personal circumstances. Longer term, depending on your situation, the sandpit is probably better for upgrade etc.