The alternatives are a backwards compatibility break (i.e. raise exc from other_exc would suppress the context, but exc.__cause__ = other_exc would not) or else that we don't succeed in eliminating the dual use of __cause__ in the display routines.

Given that those two problems are the reason I went for the PEP 409 approach in the first place, I'm really only interested in alternative approaches that eliminate them (such as setting the flag automatically whenever __cause__ is set). If you don't like it, then we already have PEP 409's Ellipsis based implementation which meets my criteria.