You can clone with
HTTPS or Subversion.
There are some notes somewhere in the repos (probably TODO in snap-core) about this.
I need ipv6 support when binding to an address (-b "::").
Is there a workaround?
You'd have to implement it, sorry. I would gladly take a patch!
Alternatively you could play port-forwarding tricks using IPTables?
Fixed in snap-server! Thanks wladh!