At Newegg, I searched for:
NVMe backplane
These popped up:
SuperMicro BPN-SAS3-116A-N2 Backplane support 8x2.5" SAS3 HDD & 2x2.5" PCIe NVMe - Newegg.com
Supermicro BPN-SAS3-826A-N4 2U Backplane for 3.5/" HDD/SSD upto 8 x SAS3/SATA3 and 4 SAS3/SATA3/NVMe devices - Newegg.com
Supermicro BPN-SAS3-216A-N4 2U 24 Ports Hybrid Backplane support up to 20 x 2.5" SAS3/SATA3 HDD/SSD and 4x2.5" NVMe/SAS3/SATA3 Storage Devices - Newegg.com
Intel has similar backplanes -- somewhere in their product catalogs
(I've seen them, but can't put my finger on them, just now).
You might ask SuperMicro to escalate your tech support question,
because SM is obviously manufacturing NVMe backplanes (see above).
The other thing about Intel's 2.5" 750 NVMe SSDs is that they require x4 PCIe 3.0 lanes:
as such, if you are trying to join four of such SSDs into some RAID array e.g. RAID 0,
you will necessarily need 16 PCIe lanes just for that one RAID array.
One of the two thrusts of my presentation to the Storage Developer Conference
a few years ago was to allow variable transmission clocks, e.g. to "sync"
SATA-IV devices with the PCIe 3.0 standard: 8G and 128b/130b jumbo frames:
http://supremelaw.org/patents/SDC/SATA-IV.Presentation.pdf
And, likewise, SATA-V would "sync" with the 16G clock planned for PCIe 4.0.
Upping the clock rate and switching to jumbo frames extends the
logical evolution of SATA and SAS -- by mating a single PCIe lane
with a single serial data stream.
This logic becomes even more compelling with the arrival of PCIe 4.0's 16 GHz
transmission clock, and continuing with the 128b/130b jumbo frame.
As such, we should reasonably expect future SAS standards to increase their clock rate
from 12 Gb/s to 16 Gb/s, in stepwise fashion.
You will note that the SATA standards group are STILL stubbornly stuck at 6G,
while the USB 3.1 standard adopted BOTH the higher clock rate (10G)
-AND-
their own jumbo frame (128b/132b).
With a large enough on-board cache on these PCIe 3.0 SAS RAID controllers,
the need to support heavy multi-tasking workloads is being addressed robustly
by the speed and capacity of those on-board caches: those caches play
a very crucial role in the overall performance of such high-performance
RAID controllers.
Areca are another very well developed brand.
I'm exactly in agreement with you: the industry should be developing
reliable PCIe 3.0 RAID controllers with support for 2.5" NVMe SSDs,
even if a "bridge chip" is required to mediate the PCIe lane pool.
MRFS