I know of one largish bank moving away from Oracle middleware and RDMS. It's happening in pieces starting with low hanging fruit and for awhile the two will run in parallel (with the new data stores starting off as a comparison check to reconcile any bugs that crop up). Some early wins were account transaction logs that can go into better suited DBs, etc.

My understanding is that they were relatively lucky in that most of the hard parts are in the middleware layer and rarely the DB itself - the bank has been around since the 1800s, so has a huge mishmash of technologies that go from old IBM mainframes up to more modern cloud infra. So they're already kind of used to using middleware logic to stitch together various data sources.

The funny thing is that my contact there said the primary impetus is that they see the writing on the wall for a lot of their "legacy" Sun hardware, and figure if they're going to have to redo a lot of it, they may as well re-architect the rest. There'll still be oracle DBs running in the bank for a looong time, but there'll be less and less of it.