You don't seem to understand how cache works, or what caching is. RAM IS cache. It's cache for the HDD. Don't you get it?That's why I tried to be careful of my statement. I completely agree which is why I said it should almost be treated as a level of cache. In reality a small enough application will end up completely residing in L2 cache. I would see something like this working no differently by simply using another level of memory should it be available. It's just something that's between you're run of the mill SRAM cache and system memory so you kind of want a little bit of both in terms of functionality to be present at that level, if that makes any sense.
If you consider memory in general, it tends to be virtualized and pages handled by the either the OS and hardware depending on the level. From a logical level, I would want it to be in the same domain as RAM but in the case of using more than what's on the CPU I would want it to act like a cache if there is external memory. I guess that's what I mean by kind of like system memory but kind of like cache.
Caching is simply a matter of preloading data so it can be accessed faster.
If you believe the only type of cache is on the CPU, it isn't.
I said this yesterday why database servers have so much RAM, the files are cached from the HDD into RAM. That is caching. Man talking to you is like talking to a wall.