With the way Apple ARM architecture is desiged currently the Mac Pro ARM will either be a non-upgradeable unit all in one.
or
hear me out...
ACSP servicable or perhaps even end user replaceable main logic board on a caddy (think of the cMP 4,1-5,1 CPU boards).
secondary RAID storage for additional local storage comprising of SSD drives. (not 3.5") but m.2 or some other factor.
Am I crazy?
A little crazy.
If you take the bulk of the main logic board and turn it into a horizital/vertical (tower / rack ) plug in card then it won't fit inside the case. You would have perturbed the internals so that would have flipped a tower board into a rack enclosure board and vice versa.
Nor would it control costs an any significant way as who have an extremely complex , proprietary socket to plug the board into and a board with lots of stuff on it. The Apple SoC is a 'system on a chip" so there are a wide variety of different types of communications channels coming off the package. All with different standard versions evolutionary cycles. . The wider the diversity the more long term brittle that connector is likely to be.
The 4,1-5,1 main logic boards had the I/O 'Southbridge' chip with large diverse communication fan out on the main board ( and not on the plug in tray). The M-series chip largely subsumes all of that. T2 , PCH chipset , Thunderbolt controllers, display output controllers
all get pulled into the "system on a chip".
That will put very high tension to pull the back edge TB ports, video out , and primary boot SSD all onto the tray along with the RAM. Fighting that tension just gets you a more and more proprietary and long term change brittle connector back to the base board.
People want the old 4,1-5,1 tray to come back but where the subcomponents are on the old 4,1-5,1 board moved significantly.
PCI-e fan out could primarily be done from a base board PLEX switch , but when PCI-e v5 , CXL 2 , etc come along probably not going to be "future proof" viable.
What is more likely to fail and need a ACSP work is people 'blowing up' their Type-C , Type-A ports. Apple is already routinely using micro-boards to cover the ports, so when they get physically damaged the primarily logic board says the same and just replace the Port and the associated PHY chips at relatively low cost.
Apple's SSD ( as well as practically all other desktop/high end lapotp (i.e. non MMC drive) ) already use aspects of RAID internally anyway. If the write speeds are very close to the read speeds of the SSD, then it is using RAID internally already. Apple doesn't need any fancy or custom RAID SSD facility on the main or tray logicboard any more than what the standard Apple SSD controller provides. Nor do they need chiplet building blocks that drag in largely redundant SSD controllers and secure elements with each die/tile. That's is largely dubious. The Apple SSD has a bunch of boot security elements built into it that doesn't particularly need tons of redundancy or high duplication for vast majority of workloads. Users need backups if there is an fundamental Apple SSD problem. failure; not more drives with a single point of the exact same failure mode.
