The strategy I used for pysrp and csrp was to just select a few Prime,Generator pairs from RFC 5054 (1024, 2048, 4096, & 8192) and provide those as options to the user. Similarly, the hash algorithm is selectable from SHA1, SHA224, SHA256, SHA384, and SHA512. In those implementations, the choices aren't sent over the wire. It's expected that the choice will either be hard-coded into the application or that they'll negotiate the ((Prime,Generator), hash_algorithm) selection prior to attempting SRP authentication.

There might be advantages to supporting hash algorithms other than SHA but it seems to be the industry standard and no one has yet complained about the lack of choice. Though that could just be a side effect of having a small user base. It's impossible to tell how many people are using it.