There is no need to upgrade chambers or “certify” any modern action. It’s simple. If an action is offered in a Magnum boltface, or is offered in 308win, as an example, it can be safely loaded to the same pressure standards when firing the 7x57. The barrel predominantly cares only about wall thickness and max pressure, and the receiver only cares about case head diameter and max pressure (bolt thrust), such if an action is chambered for the same or a larger diameter cartridge at a higher pressure standard, it is well understood it can be loaded similarly in the 7x57.
Doing so absolutely does not solve the continually waning popularity of the 7maus.
The 7x57 has never enjoyed broad appeal, in large part due to lacking global trade and subsequently, geopolitical and national biases. In the early era of the 6.5x55 and 7x57 Mausers, there simply was not a sufficiently established global economy to have sustained the foreign cartridges in the US - unfortunately, since the “best idea we had” in the US at the time was a sad ballistic excuse of a cartridge. Global trade accelerated, however, two World Wars drove anti-German sentiment, and of course, in short order following WWII, we saw the advent of the American version, the 7-08.
So in more recent generations less influenced by post-war biases, the decision to adopt the 7x57maus is largely foolish: a buyer must be significantly otherwise motivated to purchase a mid-length cartridge with relatively low rifle, ammo, and brass availability, which requires handloading or boutique/custom ammo to meet the performance of an American designed version which is highly available. So the question really isn’t “why don’t more people buy 7x57’s?” it’s really a question of, “why would they buy a 7x57 over a 7-08?”
Without a sufficiently popular and satisfactory answer to that question, the 7x57 will never do anything except fade more and more. It’ll never disappear, not in the proximal future, but it certainly has no reason to expect a swell any time soon.