It was a good catch after all, indeed it should not segfault and now should be fixed.
Yesterday I didn't have time to add here the comments about it, but as jsonrpcs replaced the mi_fifo, its default transports were changed in 5.0, given that xhttp is not loaded by default.
I also added a note in the upgrade guide from 4.4 to 5.0. Thanks for assisting with troubleshooting.