We are now working on source address validation technologies for intra-domain and inter-domain networks, aiming at overcoming the improper block or improper permit problems of existing uRPF technology. We will have a BoF meeting on this topic in IETF 113 (refer to https://datatracker.ietf.org/doc/bofreq-li-sav-for-intra-and-inter-domain-networks/). We also created a mailing list in IETF (firstname.lastname@example.org) for discussion. The subscription portal of the mailing list is https://www.ietf.org/mailman/listinfo/savnet.
If you have interest in this topic, you are welcome to join the mailing list and attend the BoF.