Disclosure EMCer here.
Chris - I agree that SDS is an over-used term (I think we're more than guilty of "software-defined *" labelling - so trying to call the kettle black, but rather maybe add to the dialog).
I hate to say it, but I beat you to a rant on this topic :-)
It's worth a read "Is the dress white and gold, or blue and black?":
The fascinating thing for me (coming from talking to customers every day all around the globe) - the "illogical circle" I put in that post is UNIVERSAL (silly humans! :-)
We have 3 data planes at EMC/VMware that are absolutely, definitively SDS (sold without hardware): transactional = ScaleIO/VSAN; object/HDFS(and soon light NFS) = ECS Software. The "illogical circle" (though I get it) after a ton of conversations is that while those are ABSOLUTELY available in a software-only version, the customer desire for integrated consumption + support drives them to appliance (commodity hardware packaged with the software) consumption. Examples of this form of "packaging": ScaleIO = VxRack with open persona, VSPEX Blue/VSAN ready nodes = VSAN, ECS = ECS appliance.
We have 1 control plane at EMC that are absolutely, definitively SDS: the ViPR Controller (and the open-source trunk is CoprHD).
Netting out this first point - there is a real SDS, but to your point, that's not a sufficient discriptor - you need to pull out the clarifying points you raise. Netting out the second point - most customers in my experience like to play with SDS in a "bring your own hardware" model - but when they move forward for real, they tend to prefer appliance consumption (I wonder if Nutanix would be willing to share the ratio of appliance vs. software-only - I would suspect it would match my observations for our stuff).
There's a 3rd point.
NOW, we ALSO have "virtualized versions of our appliances" (vVNX - analogous to ONTAP Edge, but I wouldn't call that SDS, as it's a software version of something built around an appliance - and then is hobbled by the fact that hardware dependencies (in the vVNX - and I believe ONTAP Edge - cases the hardware necessary for HA clustering with any modicum of performance) limits their use cases. Likewise - there is a virtual Isilon node, but the current version again has a dependency (in this case, the NVRAM that exists in an Isilon physical node. There are also software-only XtremIO and VMAX - but not available in the wild.
Each of those case, YES, it's commodity hardware, but the reason it's really only available in physical appliance form (or hobbled software-only form) is a esoteric hardware dependency. This means that I think calling them (or other examples of that) "SDS" is a huge stretch.
**IF** we were to solve for the Isilon NVRAM dependency and make an Isilon true software only stack (vs the virtual Isilon), then I think it could be called SDS.
BTW - all the SDS stacks and virtual appliances are available for download in a free and frictionless way (just Google them).
Anyone calling something that you can ONLY get in something with strict hardware dependencies - well, that's just silly marketing driven off the ledge :-)
So - to net out my POV:
1) - True SDS data plane and control plane stacks have NO hardware dependency, but WHAT that SDS stack does is wildly variant - calling it "SDS" and thinking that's enough is stupid.
2) - That with the exception of the ULTRA large enterprises (think 100's of thousands of VMs, 100's of PB) and the hyper-scale folks - customers in **PRACTICE** don't have (and don't desire) the ability to manage bare metal hardware/firmware/support with SDS stacks - and the SDS consumption model that tends to be the most popular is packaged with hardware
3) - That Virtual Appliance forms of hardware appliances (usually hobbled) - it's a stretch to call those SDS.
4) - That trying to "SDS wash" a hardware appliance is just stupid :-)
Thanks as always for the dialog!