First of all it depends on the customer deployment scenario.

Secondly, having an issue with number 2 cloud provider at world scale?

Or would you rather have AWS?

That's not what I meant to say. It doesn't matter which cloud provider at all, if the product running on it is an emulation. All the assurances you spoke of regarding early Burroughs Large Systems resulted from hardware/software co-design. The hardware does not exist anymore. They ported some abstraction layer by whichever means to contemporary platforms, and now top that by making it available to the cloud, saying: 'Diz iz good! We king of the mainframe hill, Ugga Ugga!'

I wouldn't trust that. The same way I wouldn't trust that from another, very established competing vendor, saying the same things, having the same nimbus of security and reliability.

Because sometimes there are blips on my radar, wherein some conference talk pops up, and people looked under the rugs of these systems, not even hard, just casually, and discovered some oopsies.

So it seems like that nimbus of security and reliability is more a result of very careful isolation from public networks on one hand, and inacessability for the bored and curious pranksters of the world on the other. But it is no absolute.

Especially if it's running in emulation on contemporary COTS hardware. (In the EFFING cloud!)

Just my not so humble opinion, though.