To me abstraction above the hardware is like condoms. Some people say "Use three condoms, its better".
I don't want a literal C64 -- just the complete open simple access... but 64-bit and 3Ghz and multicored.
I don't want it to run on a 386, just x86_64.
Nothing quite so stark and sublime as hacking away with registers and memory alone, eh? Ring 0 is pretty cool place to be, I'll grant you that.
I think perhaps what I long for is the knowledge that I could gain a _total understanding_ of the hardware, ROM, timings - things were simple enough back in the day. The commodore 64 and other 8-bits are like that, and I've seen talks given on the c64 that seemed to lay bare every secret. I have so much respect for those hackers that know a device through and through with history and anecdotes related to the thing to add color to their own vast understanding.