Here's what's going on.
The industry is opening up, there are opportunities at "upline" airlines like the legacies and places like JetBlue and the freight carriers. So captains, who have been stuck at Mesa 6+ years are moving on. Nobody really knows how many captains are moving on, people on mesahub are convinced it's in the hundreds, That's not correct and I have the seniority number movement to prove it.
There are a few FOs who are taking the opportunity to move to other regionals as FOs. Some of them are doing it for good reasons, there are now opportunities at those regionals that were not open to them before and that regional is a better fit for them. Some FOs are chasing a "quicker" upgrade because they think upgrades at Mesa have slowed down. If that works for them then good luck, but at best that's a crapshoot. Nobody has a CLUE how many actual FOs are quitting, it's bigger than zero, but I don't think it's much bigger myself.
It's harder for Mesa to fill new hire classes, just as it is at any regional right now, and Mesa, being stunningly cheap, isn't offering the same bonuses to new hires and even if they were the companies reputation precedes them so it's not like Mesa is most people's number one choice.
The next year will be interesting, certainly upgrades will pick up as captains move on - even if its 10-20 captains a month, you have to backfill those eventually. If the company isn't replacing FOs at the same rate, which were arguably in short supply at Mesa anyway, then that's going to make it even harder. On the other hand US Air is drawing down 1 plane every 6 months and the Dash program in JFK has collapsed and I'm not so sure that Mesa can win the jet flying that will replace it. So that's a pool of pilots who will probably replaces Dash pilots out West who will then upgrade into the jet.
I don't think Mesa will collapse, the same doomsayers over on mesahub having been saying Mesa is going to collapse for the past 2 years, and they haven't been right about any of that yet. It will be interesting, but it's going to be interesting at the other regionals as well. Republic/Chatauqua has taken on a lot of flying and Bedford has proven he can run an organisation into the ground with the best of them. I hear that SkyWest is struggling to handle it's growth and keeping up with hiring. Pinnacle, Colgan, Mesaba et. al., who knows whats going on there. Comair, still lives and dies on how mother Delta turns and coughs. So mostly it's the same across the industry.
If Mesa is the right fit for you, which mostly means you'd live in your Mesa domicile as opposed to commuting somewhere else, then there's no good reason not to go there, because if any of us could predict the future of any regional with much certainty we'd be making out money in the stock market and not flying planes. If you wouldn't consider Mesa in the first place, no good reason to consider it now.