IBM has two architectures which are de-facto only used by them, s390x and ppc64le. They have poured a lot of resources into having open source software support those targets, and this announcement might mean they find it easier/cheaper going forward to virtualize ARM instead and maybe even migrate slowly to ARM.

I think they see customers wanting to have the flexibility to move to ARM and this is the fastest way to say they support ARM workloads. Maybe this is a path for IBM to eventually use ARM chips down the road, but I see this as being more about meeting customers where they think the demand is today rather than an explicit guess for tomorrow.

ppc64le has other machines. Raptor off the top of my head, but there's also that weird notebook project that seems to be talked about once every few years and probably won't ever happen and some pretty cool stuff in the amiga space (I don't know if that's strictly le but power is supposed to be bi-endian)