It sounds to me from a lock-in standpoint the Nutanix solution is far more lock in then a software-only solution like VSAN. They admit it themselves they want to be and end to end solution provider- so you are locked into their solution.
Not that there is a problem with lock-in, just seems sort of hypocritical to call out VMware as lock in when guess what, Nutanix is lock in too.
The approach these two players are taking is certainly interesting, myself I still have tons of concerns on how well it works, what they are trying to do is incredibly complicated to get right, assuming it's even possible(or perhaps more specifically if it's even a worthwhile exercise).
It would not surprise me in the end if both of these companies toss their integrated compute capabilities (or put them at the low end of the market ala HP Storevirtual VSA) and shift focus almost entirely to distributed grid storage, and most customers end up with separate(but more optimized) compute and storage stacks.
They would still have a very compelling solution(on paper), and theoretically there would be significantly less risk and complexity to managing deployments. Also likely higher margins too, storage tends to have much higher margins than compute servers and companies seem to like margin.