I don’t think intermittent connection can be more than an inconvenience for clients.
Vaults, however, do need a stable connection, so we’d have to wait for a sufficient level of saturation for them to work through a mesh network, even in cities. Also, the connection level protocol will need to (or maybe it already can) handle roaming: I would be accepted as myself even if I’m connecting from a new IP address. QUIC (mentioned here) for example is a transport protocol built on top of UDP, and it uses proper sessions instead of IP address/port combinations, so it may help with that.