Wrong! The Silicon Graphics O2 has a unified memory architecture, yet it features
- eight RAM slots,
- an upgradable CPU (on a daughter board, one may even upgrade from the R5000/R7000 generation to a R10000 or R12000 MIPS CPU),
- one industry-standard PCI-X slot,
- two slots for user-replaceable HDDs (standard 80-pin SCA connector, while not the most common interface it lets you use non-SGI-rebranded drives),
- an interchangeable AV module (just audio or audio + video capture).
The O2 was a stylish, low cost (for the manufacturer… let's say "low
er cost") workstation with amazing capabilities thanks to its unified memory architecture (real-time background replacement in a live video stream was a big "wow!" in the mid-90's). As outlined, above, it was perfectly upgradable, and very easy to service (just pull at tab and the motherboard slides out on its tray…) although some parts were proprietary and came at SGI prices (aargh! 239-pin SDRAM modules).
If Apple can pull out a mini-Mac Pro that fits every item of the above description (stylish,
relatively low cost, amazingly capable, upgradable) with modern equivalents (say, DDR5 RDIMM,
E1.S storage and the SoC on some Apple proprietary variant of an
OAM GPU module), it will be a cult machine, just like the O2.