somebody is going to want cash in

Maybe. The hard drive makers have long experience with boom-bust cycles. They are likely trying to figure out if this is real, or just a blip and in a two years (when the new factory opens!) demand drops again.

If there is new capacity in the future my guess (guess!) is that this is a case of a new factory to replace the old, and they just keep running the old for another year instead of scrapping it right away.