The only universal answer: a spiral with zero in the middle. I kid, mostly.
For UI about memory, I would honestly go with the conventions for other UIs about memory like hexdumps, where smaller-numbered addresses are at the top of the page and proceed down, usually with a little bit of LTR or RTL within 16 byte blocks or so (possibly worth localizing?).
Unless you really want to innovate the UI, in which case do whatever. They're just numbers. You can use any consistent ordering, and they've all been used for something, so there's not a firm precedent. I think bringing in endianness, 2d cartesian coordinates, etc is a bit of a red herring. I'd only caution that trying to have numbers that grow up and sideways like a cartesian graph will be really confusing, just because if it's embedded in a UI that reads topdown/LTR like English, it'll be really hard to avoid applying that to the memory UI too.
If you want to do something weird, I guess there's also the good ol' space-filling curve visualization; that'll keep things compact without privileging any direction or even either end of the ordering too much, at the cost of, well, being weird.