Mesa upgrades
With the new United deal, Mesa is looking to add around 55 jets to the fleet, beyond the original growth plans, so I would imagine there will be some good movement for a while.
Obviously, the quickest upgrades will be in the Beeches at AMW, with the lower seniority. However, there will probably be other opportunities if one is in another aircraft. As I posted above, the new contract does not allow a person to bid from a prop F/O position to a jet F/O position, nor does it allow a Beech F/O or Dash F/O to bid to the captain seat of the other turboprop, nor does it allow a jet F/O to bid to any prop position. This means that only Beech F/O's can fill Beech captain seats, and only Dash F/O's can fill Dash captain seats, which might help each upgrade a bit quicker.
Another consideration is that the 18-month seat lock for new Beech and Dash captains will allow more junior jet F/O's to get the jump on upgrading to jet captain ahead of prop folk.
These are just some rambling thoughts. Actually, it's all pretty convoluted, and people I've spoken with at Mesa aren't even sure how it will all play out. Whatever equipment your buddy starts in, it's a good time to get into Mesa, as it's now entering a cycle of real movement in all equipment types.