If they're like most places, they're going to front-line support and/or front-line development.

Banks and other institutions with a massive legacy codebase and/or infrastructure are keenly aware of how much it costs them to maintain, COBOL code on zSeries. They'd very much like to replace the currently-irreplaceable mainframe wizards with interchangeable "full stack developers" that they can outsource or subcontract to.

There's a lot of Gen-X and Millenial managers that really struggle with having whole chunks of their infrastructure that they can't commodify (source: am a Gen-X IT manager). Part of this is a legit concern: COBOL+zSeries or RPG+iSeries devs are not exactly common, and they take a long time to train up. Senior architects are even rarer, and most of them are a heartbeat away from their, ahem, last promotion, so it makes sense to try and move that you can to something that you can more easily support.

The other part of this is that there is a type of insecure douchebag manager that hates having indispensable employees, and there's nothing as indispensable as the greybeard who knows the COBOL code that your billion-dollar company runs on.