One difference between uni-arch clusters, as we know them today, and multi-arch clusters, is that migration won't be supported (no migration between nodes that have different architectures), which will require us to avoid migration tests on multi-arch clusters.
This includes tests that indirectly involve migration, for example interface hot-plug (existing feature), or NAD swap (in-progress for 4.22).
However, the work to disable these tests is quite minimal. in a scale of marking such tests+addressing the marker in the DevOps test-runs configuration files.