Ah, the Mainframe...
Sure HCI systems are possible solutions for really stand-alone (silo-ed) applications. As soon as someone says I need that information from that silo-ed environment, the fun begins.
Mentioning mainframe brings back some very salient points regarding how they (at least IBM and compatibles) worked....partitions(I suppose modern speak containers) that could even communicate with each other, pass information, have differing priorities etc, let alone discuss mainframe virtualization technologies that still kick the crap out of any x86 offering.
Let's get Cloud out of the way as well, all it effectively is, is a Computer Bureau on steroids, with infinitely better network connectivity.
Enough of a rant...beer time and nostalgia.