> Last time I checked when I hotspotted my T-Mobile (US) phone, hotspot clients got only an IPv6 address, with 6to4 [edit: no, NAT64] translation used to reach IPv4 addresses.
You would have the same problem without IPv6 - your phone doesn't have a spare IPv4 address to give out, it would have to give you some kind of internal-only address and then NAT it when talking to the public internet.
> This breaks OpenVPN, which insists on both endpoints being one or the other.
That seems unlikely (also why would your server not have a v6 address?). You can't connect to IPv4 addresses by IP because you don't have an IPv4 connection, but connecting to your server by hostname or by v4-address-embedded-in-v6-address should work.
