Not sure if it's been discussed or not but a good idea for Apple would be to release an internal Thunderbolt 4 drive chassis able to be raided, it would really push the MacPro ahead of the other manufacturers (Dell & HP)
It is doubtful this will become a wide spread practice among system vendors. Part of the usefulness of Thunderbolt (TB) is to transform internal system signals (PCI-e ) into something that can be used to communicate between boxes. If you put the external peripheral box inside the original computer system box, it is now internal. The normal internal connectivity is both cheaper (there are already PCI-e lanes inside the box) and less complicated.
Indeed many of the initial TB products are either PCI-e cards wrapped in a "new" package or PCI-e cards + old external box (e.g., an eSATA PCI-e card moved to the external box). If go the other way there is no need for TB or the external boxes "inter-box communication" infrastructure.
Very similar rationale as to why there will never be native TB drives. You'll have either PCI-e or SATA drives but there aren't going to be "native" TB drives ( or likely any other perhiperal for that matter. ) TB will always be hooked to something that is PCI-e or DisplayPort "native" or has in standards based , inexpensive controller that makes it PCI-e or Display Port "native" (e.g., SATA-PCIe controller. ). TB isn't going to "Drive out" the older standards. It will make them useful in more places which only means they will continue; not disappear.
PCI-e is faster than TB if lash up sufficient lanes. It always will be. There is no "speed" advantage to a TB drive versus one on PCI-e.
and maybe use internal mSSD or chips similar to the MacBook Air for the boot drive, either that or a an option for an oem version of the OCZ PCIe SSD cards, slight redesign case to match.
Actually more the case of a internal SSD similar to that of the XServe. The XServe has a SSD boot drive option long before the MacBookAir did. Probably would want to use standard mSSD drive at this point though as opposed to the custom drive that Apple used in the XServe.
There are a couple of features from the XServe: easier horizontal rackmount, front accessible drives that lock in place , and this SSD boot drive that could be moved down to the Mac Pro to expand its usage range without significantly impacting the historical primary usage profiles.
A front panel with two lockable 2.5" drive sleds might kill two birds with one stone ( front drives and SSD ).
As far as mid-full size SSD drive card though. There is no pressing need for Apple to do that in a standard or even BTO config. Apple should work with vendors to see that they work, but an "Apple labeled" one isn't necessary. Neither is an Apple labeled RAID card. It is time for Apple to leave that too (single or dual SSD, SATA III drives are going to replace a large fraction of the internal "need for speed" RAID set ups and external RAID set ups have lots of competitive offerings to choose from when need external bulk storage. ). Given the internal core chipset has more than a few high speed SATA lanes and decent RAID abilities, an additional card doesn't have alot of traction when targeting the internal drive sleds.