I see the value proposition that this has in the particular case of Framework where you update certain parts, but the vast majority of laptops cannot have any change beside the RAM (if you're lucky) and the storage (same).
So in those situations, the best PC case is the one you already have: the laptop.
The idea is that you have a spare mainboard laying around if you've upgraded. A cheap $40 case is a great way of putting that hardware to use.
And while many may not want the hassle, there's plenty of value for a home server with an external storage drive for a lot of people.
Also, don’t look a gift horse in the mouth. Framework have basically given us what we’ve always wanted in a laptop. Just say thanks and buy one the next time you need a laptop.