If you own the hardware I imagine much of your PHP/html stuff will be served from the file system cache much of the time so you probably wouldn't see much benefit...

The idea would be to do it in an ultra-minimalist setting on a VPS (something under 256MB of ram).

I don't think it would do much there either: If it fits in your left-over RAM, then it's probably in the disk cache. If it doesn't, then you can't create a RAM disk large enough.

It might help with latency for the long-tail of data that isn't used very often and thus maybe replaced in the cache by other data, but on the other hand the OS probably had a reason to replace it and forcing it to stay in RAM might slow everything down.

You'll likely have better luck configuring php-fpm and the OpCache properly, as they are going to be doing basically what you're proposing anyway, and for the OpCache it's even nicer as it avoids reparsing the code

Yea I've already set those up but I don't think opcache handles random text/html/js files. Only php files.

I could be wrong.