So a couple of things here that I've confirmed with the U.S. MSA product manager:
- The D2700 is being phased out as a JBOD for ProLiant servers, but not as a SFF expansion module for the MSA line. If I'm reading the MSA 2040 QuickSpec correctly, there's also an MSA 2040 disk enclosure.
- The reason the D3700 doesn't support the MSA 2040 isn't because it's a JBOD for ProLiant - that's also something you could do with the D2700.
- The D3700 uses the new ProLiant Smart Carriers which the MSA product does not. That is why it isn't supported as an expansion enclosure for the MSA 2040.
Hope that helps!