There is a lot of command upgrades from the big busses to the buslets(
@ib57) at the moment. But probably not enough evidenced by current rostering.
New Captains normally require a specified time on the 320 fleet before moving up a fleet(right?).
With more buslets coming (this year and next), there will be need and pressure to keep those captains where they are.
Meanwhile, big busses arrive next year and continueing for the next 3-4 years. There will not enough drivers to fly them because if GF continuely moves captains up from the 320s, eventually all the 320 captains will be blueliners. Not ideal.
I think there might be a need to upgrade 'any' First Officer who meets command requirements, regardless of where they are on the seniority. All of these guys will be on the 320s.
When these guys are depleted, that's the point where I think GF will bring in DECs for the 330/340s.