If Nvidia has the capability to make a differentiated mining product, shouldn't that be enough to get miners to go for it? Why halve the hashing rate on the "gaming" GPU artificially? If it is a supply issue, shouldn't Nvidia, as a company, try and solve for it directly (maybe it is really hard?), instead of making their products unattractive to a certain set of customers?
The same criticisms were given last time nividia tried to make a mining card and obviously it didn't work as last time they didn't need to use artificial limits.
This makes the problem of designing specialised mining cards equivalent to designing fast and efficient DRAM, an area where the consumer product is the cutting edge. This was by design to reduce hashrate centralisation.
Even the latest ethereum ASICs are only 10% more efficient, cost much more and can only mine ethash and its variants.
So as it stands I see no evidence that suggests mining cards will be cheaper with better efficiency, especially when the cryptocurrency community slowly moving away from mining.