This 'N' That
Disclosure: I work for VMware in the EVO:RAIL Team :-)
Interesting post. Firstly, I'm not sure if an all-flash based system is requirement to make hyper-converged a true alternatively to conventional SAN storage. So long as the working set (r/w) remains in cache, and writes are de-staged to disk - its not clear to me why an all-flash array or all-flash hyper-converged system would be that compelling. Unless the customer has very deep pockets, and wants an absolute cast-iron guarantee that they would limited by a spindle. Of course, the are customers like that - otherwise these products wouldn't exist. As you rightly say, for the cost per GB, you would need a very compelling use-case...
As with all these things - whether a technology can truely upset the market depends largely on the use-case. The customers see value in both conventional server/switch/storage - which allows them to add additional disk shelves for increased capacity - without buying more compute (that they may not need) - in what would be a classic scale-up play... Where they see value in hyper-converged is in SMB, ROBO and VDI - where they want an easy deployment option with relatively low on ramp compared to other infrastructures - and where the compute and storage requirement scale out at the same rate - as is the case with VDI.
I'm not sure you analysis of the other vendors passes muster in all cases...
Cisco - have recently signed a distribution deal with Simplivity
Dell - is both an VMware EVO:RAIL Qualified Partner and also Nutanix supplier - in the main both a hybrid models of SSD/HDD
EMC - Will have an VMware EVO:RAIL system by Q1 of next year, they also offer Scale IO as server SAN (although I see you mention that...)