I think this is a golden opportunity for those who want to progress their aviation career with a major airline like KA on the -400. If you are a struggling GA pilot wanting to get a break or get their foot in the door, what do you got to lose. Certainly the pay is much much better then what you are on now. Yes, I understand and I do agree one has to protect their earning capacity and not allow it to be degraded. However (from a GA pilot point of view) if you are offered a chance to fly the big jet would you consider not to join and miss this opporturnity for a career progression.
If you join are you going to be black listed by the IFALPA? In my opinion I think it is unfair to those who want to progress their career.