Although apple doesn’t publicise the fact all that much on the new Mac Pro coming later this year, it does actually have two SATA ports and some 8 pin power connectors. Apple don’t provide the necessary “cage” to mount the drives (at least as far as we know so far), but third parties have already announced some products that mount internally and use these ports to connect a bunch of disks.
As for power, I believe the two MPX bays provide dual 8pin connectors for up to an extra 300 watts, so should support most power hungry pci-e card designs.
Honestly though, if you can afford this machine it’s not like really any of this matters, this isn’t exactly a hobbyist computer people are going to buy and upgrade themselves all that much.
They haven’t announced the maximum amount of flash drive space you can get from them (and I wouldn’t pay Apple prices for it anyway), but you can get 4TB of overpriced SSD storage on the current iMac Pro.
As for power, I believe the two MPX bays provide dual 8pin connectors for up to an extra 300 watts, so should support most power hungry pci-e card designs.
Honestly though, if you can afford this machine it’s not like really any of this matters, this isn’t exactly a hobbyist computer people are going to buy and upgrade themselves all that much.