People on reddit have gone from 1700X to 5800X3D. I guess you are correct in saying that this many generations skipping on the same mobo has never been possible in history before and may never again be possible. Mobo makers are surely not happy about the loss of sales.
The 5800X3D is not a good investment with Zen 4 around the corner. If they sold it for $250, different story. I would say a 5600, 5600X, 5700x is the only thing people should upgrade to. The 5900x when it's in the mid to low $300's somewhere for content creators. Others would argue 5950x for any video editing or encoding.
I should point out that my B350 Carbon Gaming Pro is the flagship of the B350 boards. Top of the line and the same in every way to the X370 Gaming Pro Carbon minus the chipset. MSI has been great because my board could run every memory stick in the beginning with no issues. When I went past 3600mhz, it would run 3733mhz and I would get weird crashes and restarts without blue screens. At 3800mhz it would boot and usually crash withing a few minutes. The new Agesa 1.2.0.7 seems to have solved all the memory issues up to 3800mhz. That should have been fixed several years ago.
The B-450/X-470 boards has no issues with memory timings up to 3800mhz. I have said for years flip a coin between MSI and Asus. They are both excellent on AMD and have been great for me for a couple of decades on Intel.
I am the guy who told people to buy the Hynix CRJ 3600mhz kits and call it a day 2 years ago. Credit to DrMrLordX for pointing me to the E-die (e-revision) Micron sticks. The CRJ sticks do 16-20-20-20 @3800mhz 1.37v all day. Some of these memory OC'ers think that running memory @ 1.5v to start is the way. I am not one of those type of Oc'ers. My E-die sticks are @ 1.42v.
I put my very early B-die sticks back in the drawer. Mostly because they were 4GB modules 2x4GB. They could run 14-15-15 but they crapped out just below 3600mhz. So I went with my CRJ 16GB 2x8GB 3600mhz kit.