Typically I’ve seen a motherboard supports about 2 generations of gpu before some underlying technology makes it no longer can keep up.

If you are going from a 30 series to a 50 series gpu there is going to be a need for increased pci bandwidth in terms of lanes and pcie- spec for it to be fully utilized.

I just saw this play out with a coworker where he replaced 2x3090 with a 5090. The single card is faster but now the he can’t fully task his storage and gpu at the same time due to pci-lane limits. So it’s a new motherboard, which needs a new cpu which needs new ram.

Basically a 2 generation gpu upgrade needs a whole new system.

Each generation of pcie doubles bandwith so a future 2x pcie-6 gpu will need an 8x pcie 4 worth of bandwidth.

Even then gpu’s and cpu have been getting more power hungry. Unless you over spec your psu there is a reasonable chance once you get past 2 gpu generations you need a bigger Psu. Power supplies are wear items. They continue to function, but may not provide power as cleanly when you get to 5+ years of continuous use.

Sure you can keep the case and psu but literally everything else will run thunderbolt or usb-c without penalties.

At this point why not run storage outside the box for anything sizeable? Anything fast runs on nvme internal.