I'm not so sure it's a shortage, but rather regional guys seeing the writing on the wall and switching to either 135/cargo to get PIC time.. Or possibly heading overseas?
There may be a shortage at the regionals, but only a self induced shortage due to their low QOL... We've got probably 12 guys at my 135 who could easily get on with a regional but make more and have a better QOL flying a small turbo-prop....They are probably 3-4000hr guys, none have any jet time, but aren't even considering a regional. And never will. Of course without any glass/jet time their options will be limited in the future..I'm a little luckier in that this is a part time thing for me until something opens up, and I've already checked the boxes with FMS/Glass/Jet PIC time etc.