Who sold all these cards to this one guy?
Looks like society as a whole might need a law (at least temporarily in the first months of a new product release) saying you can't have more than 10 of the latest "gaming" GPUs from one series (like the RTX 3000 series) under one roof without special approval from nVidia, AMD, and soon to be Intel. Special permission would be to allow for things like gaming conventions, cloud gaming, resellers, etc.
I figure 10 is probably enough to have a couple of each new model in a series for test labs and reviewers.
Otherwise if you need more than 10 GPUs for a project then you need to buy their workstation cards or get special permission.
And who do you suppose is going to police the buying of mass numbers of cards from illegal operations like the tractor trailors, train cars, containers and loading dock thefts that happen where hundreds or thousands of cards disappear at one time and are then resold, presumably to the very people you suggest that manufacturers (Who rarely sell directly to the public anyhow, so would really have no stake in monitoring the suggested rationing allotment) ought to be limiting, so that it doesn't happen?
What IS realistically viable, is the idea that the monitoring of unusual electrical consumption, no different than what government agencies have done for years to find grow and drug operations, that will lead them to presumed mining operations, could actually create some change IF a law were passed saying that, say, unlicensed operations cannot have more than say 20-50 cards in use for mining and make the licensing process a limited opportunity much like what has been done for most legal grow operations. Further, even those operations could be capped at a much more reasonable number than what we've seen at many of these ridiculously expansive sites. Allow a maximum of say 200 cards for licensed operations and allow a limited number of licenses per capita or per region or whatever. And enforce it.
Or, HIGHLY tax the heck out of it and create prohibitive fines and penalties including jail time for violators. There are solutions that can effect change if anybody actually wanted to pursue them. As it stands right now, retailers are the biggest culprits in allowing cards to end up where they don't belong, IMO, as the majority of cards go through the hands of retailers from board partners. Very few cards, by comparison, are ever sold directly to the public by AMD or Nvidia and Intel is a non-player in this situation for the most part, for now anyhow. Some come through those channels, but nowhere near what is sold through board partners and retailers.