I know it has been done in the past, but I don't see us rapidly parking an entire fleet type. We have quite a few 756s, 320s, and even 777s that are 25ish years old. I count 21 757s, 21 767s, 30 320s, and 5 777s that are hitting 25 years old or more as of right now. We could retire/part out older jets piecemeal as they approach heavy checks and such, including some problem children younger than 25 (any jet I've landed has probably never flown the same since).

It seems to me the benefit of slicing down fleets like this is that it reduces the number of potential displacements. That is, if we retired a dozen 756s tomorrow the number of CAs affected would be muted by retirements, and the junior FOs being displaced would only be able to bid to 320/737.

Having never witnessed this process first hand or being privy to fleet decision making considerations, this is just idle speculation on my part. I'd be very interested to learn more from folks with better insight or hard earned experience.