Does this problem also apply to data links (from my experience I’ve never had issues maintaining a data connection despite roaming between cells and even countries)? If not then I don’t see how this effort is worthwhile.
"The solution we are implementing is inspired by the actual social and physical structure that we aim to service: each village in Oaxaca has their own fully independent core network stack, and each community is fully in charge of their own infrastructure. There is no central authority governing across communities, by deliberate choice. Because the infrastructure is operated in remote rural areas, often from a pole on a hill crest running on solar panels, and with directional wifi over large distances, network links between villages can be unstable."
If you think LTE (4G), then everything is already a data link at first sight; but most carriers still use CSFB, where the voice calls fall back to a 2G RAN.
Once new architecture exists and is proven to converge at scale, then homing a subscriber data connection through one mechanism or another (GTP, PMIP, ..., wireguard?) is just a technical choice.