Yeah even the $2 offer from JLC has me worried about it.
The PCB market is getting way too saturated and seams like they are desperate to get costumers. At some point the whole thing is going to break down and result in something similar to the recent "great ceramic capacitor shortage"
I doubt it, some of them will go under/bankrupt and the others will get more business which makes them less likely to go under themselves. It's all self correcting.
For a Great PCB Shortage you'd need to have two factors happening at once.
Like a few of the major PCB companies going under and the demand for PCBs to reduce at the same time.
eg, maybe some new 3D printer tech comes along and suddenly everyone gets the ability to print perfectly solderable copper tracks onto a bare pcb. (ok, maybe that's a bit unlikely, but you get the idea.)