As someone that follows This Week In Matrix, is there likely to be a major shuffle in the next few weeks regarding calling configuration for self-hosting? I see that there is work being done, thoug I'm not sure how much that will affect server operators

no, there shouldn't be; MatrixRTC calling has finally (after only 5 years of iteration :) stabilised. The biggest change is renaming the APIs from unstable to stable URL prefixes, but this should be invisible.