Wouldn't the easy answer to this be increased efficiency of RAM usage?

RAM being plentiful and cheap led to a lot of software development being very RAM-unaware, allowing the inefficiencies of programs to be mostly obfuscated from the user. If RAM prices continue rising, the semi-apocalytic consumer fiction you've spun here would require that developers not change their behaviors when it comes to software they write. There will be an equillibrium in the market that still allows the entry of consumer PC's it will just mean devices people buy will have less available RAM than is typical. The demand will eventually match up to the change in supply as is typical of supply/demand issues and not continuously rise into an infinite horizon.