This only works well if you can negotiate an acceptable SLA, your main vendor doesn't balk when integrating with subcontractors or other vendors and if you have a rock-solid vendor manager on your side enforcing the SLA.
Needless to say, it often doesn't work that way.
You can hook up multiple IBM mainframes remotely and set them up to automatically ensure consistent replication of machine state to various extents depending on your reliability vs. performance tradeoffs and replication distance (latency being the issue), all the way up to active-active operation across systems.
So in other words: It works far better than the failover options most people deploy on their off the shelf servers in their self-wired racks (and yes, I run my own setup across off the shelf servers; and no, they're not nearly as redundant as a pair of IBM mainframes).
And it is an awesome thing - although I didn't realise it supported zVM these days, rather than just zOS.
In any case, you've still got two baskets, which was my point.