If, as the web site implies, the standard storage on the entry level Mac Pro will be 256Gb, well.. that's laughably inadequate.
Depends upon task assigned to the system. For boot storage for a hypervisor/virtualation set up, it is on verge of being laughably over allocated.
If the "viewer' baseline is something of a standalone FCPX or LogicX only system to be used unmodified straight out of the box, then yes it is off. But I suspect Apple has use cases lined up that aren't those two.
The iMac Pro starts off with one standard configuration and everything else is a build to order (BTO) off of that. I think can knock Apple for 'missing the boat' if that Mac Pro is set up in that same way. There should be a at least one other standard configuration. Perhaps it is 12 core and 1TB (and 48GB ) as a starting baseline. ( or 8 core , 1TB , 48GB , Vega II )
There are also going to be folks who are in the "T2 is 'bad' but I'll buy it anyway" camp. Those folks aren't going to want more than 256GB either ( and primarily boot off of something non-T2 all the time after the intial set up. similar to hypervisor just a nominal macOS maintenance OS instance installed. ).
To me this implies it will be very expensive to get it to 1Tb (the minimum I would require.
apple is relatively consistent:
new MBP 16"
512GB to 1TB $200 (per 512GB --> $400/TB rate)
1TB to 2TB $400 ( $400/TB rate )
iMac Pro
1 TB to 2TB $400 ( $400/TB rate )
iMac 27"
256GB to 1TB $400 ( $400/TB rate )
Jumping to 1TB should be in the $400 range ( which if this is MLC NAND flash isn't too far off. No credit for drive being replaced but )
Most likely the MBP 16" pricing schemes are going to be quite good indicators of how much will pay for the higher levels (i.e., similar + $$ over base system price for capacity X ).
I'm wondering how badly a PCIe card with an SSD on it would suck.
By the time you buy a decent card and a 1TB MLC SSD then probably won't beat the price. TLC or QLC drive might tip the scales back into the card + M.2 ( or 2.5" ) but for moderate boot drive it the T2 options probably won't be in the competitive ball park range.
You'll need a macOS instance on the T2 since by default the PCI-e card probably won't boot on fresh from the factory settings. So will need to boot to turn the looser optional secure boot settings off.