Even good old PCIe3 NVMe is largely useless for home systems. I remember seeing a side by side comparison video of boot and various game load times featuring then super-spiffy Samsung 960 NVMe vs a Crucial SATA SSD. There was really no difference, and in one or two cases the Crucial might have even pipped the NVMe drive. 500MB/s is plenty for office and games.
NVMe does have some improvements over SATA
beyond just throughput.
I recently got my dad a cheap NVMe drive
with Toshiba NAND and the newish Phison E12 controller
. Installed into his old Phenom II system using a $15 PCIe adapter
. He reported tremendous improvement over his old SATA drive (which admittedly was a very old 120GB model, and a poor example for performance comparison). You could probably find some synthetic benchmarks which show PCIe 2.0 is "badly limiting" his max sequential speed, but 98% of the time that's not going to come into play, and he's still reaping the vast majority of the benefits over 2.0 (which I believe tops out around 1600MB/s real-world).
Also, I can't speak to there being BIOS support in every system, but in this particular instance it was very easy (an inexpensive) to add M.2 capability. In systems which already have M.2, it should be a cakewalk to add additional ports when needed. All good stuff.