FWIW, the O2's UMA let it handle far more textures than almost any other contemporary system with reasonable performance.
Most other SGIs had single or low double-digit megabytes of texture memory, whereas the O2 could host one gigabyte of unified memory and use a huge chunk of that for textures.
O2 GPU was slower than other SGI options at the time, however it could use hilariously larger pool of memory without copying, which meant that O2 could use approaches that were punishingly hard (very tight transfer loops) or impossible (huge textures that couldn't be virtualized due to needing whole texture).
That was because unlike other GPUs at the time, O2's didn't have dedicated memory but shared the memory with CPU - way slower, but zero copies and bigger.
Arguably early home computers and workstations also used "unified memory" :D
Everything that doesn't have a discrete GPU has unified memory these days. If you're asking for something closer to the RTX Spark or Apple Silicon then look at AMD's Strix Halo systems.
I want unified but not uniform - everything can address anything, but you can add slower RAM to the system without requiring an entirely new chip. NUMA is cool.