Well, wouldn't it be possible to just bid the 200, fly the heck out of the 200, and then IF and when 900s show up on property, bid the 900...it sounds like a half-promise to entice people into bidding the 700 in training..."oh, we'll have the 700 crews fly the 900s when they get here."
Example: If I started out on the 200, and some other guy 5 classes later (with lower seniority) starts out on the 700, then a 900 shows up, can't I just outbid the 700 FO for a 900 line???