> I wonder if there's a relatively simple solution to at least most of the OPs list, all having to do with outgoing ipv6 requests, which would be proxying such (or all) requests through another computer on the network that has both ipv4 and ipv6 interfaces. Maybe that is an oversimplification.
If you have an IPv4+IPv6 capable server around, you can set it up yourself if your ISP hasn't made a proxy available. There are various NAT64 implementations you can use; running them and setting up a DNS64 server is all you need to make such a feature available. You'd probably also want to add a firewall/whitelist to prevent other abusing your NAT64 gateway, though.
If you have an IPv4+IPv6 capable server around, you can set it up yourself if your ISP hasn't made a proxy available. There are various NAT64 implementations you can use; running them and setting up a DNS64 server is all you need to make such a feature available. You'd probably also want to add a firewall/whitelist to prevent other abusing your NAT64 gateway, though.