Support for ports other than 80 and 443, v3

On the contrary; but only you can force your ISP to allow a port through.
Stop paying them to block you.

DNS challenge is still an option. And using your own self-signed cert system is yet another option.

The "problem" seems to be that your ISP is blocking port 80 and 443.
If that were not the case, you would already have a certificate.
How can LE remedy that ISP induced problem?