> - yes, your software will continue to run, because that's what the mainframe is for
Maybe if you are using zos without any niche configuration. IBM has discontinued many mainframe platforms in the past, and there's no guarantee that next year they won't approach you with a 10x markup on your renting costs, that will become 50x in a couple of years and will keep going up until you decide to stop paying.
> yes, it will scale with whatever transaction volume you need in the future, because that's what the mainframe is for
Only if you gave-up on data dependency from the beginning. Transactions here means independent data processing, with possible rollbacks, not the relational concept people got used to on databases. If one needs relational data, it won't scale. NoSQL can scale with non-relational data too, it's not an exclusivity of mainframes.
> yes, you can get 99.999999999999999% uptime, because you have reliability built into the platform in astounding depth
That one is ridiculous. Uptime is limited by business code bugs, network and power outages, integration problems, and well, all that causes 90% of the downtime on a single-server shop. All the mainframe promises is that the hardware won't be a problem.
> yes, we'll happily help develop new functionality and support your in house staff in managing this system; the mainframe can actually detect faults and arrange a service call.
Yes, mainframes come with support contracts. You can get support for other platforms too, with the advantage that you won't need to hire IBM.
Anyway, none of that changes the fact that nobody wants to start using a mainframe nowadays, and that the people using them are either looking on how to replace them or avoiding increasing their usage. IBM will certainly be able to milk that market over the medium term, even more if they keep increasing their prices. They revenue may even go up for a while. But that's not thriving.