We actually launched a service that provides you with a public IPv4 address and a /56 IPv6 block over WireGuard. It bypasses CGNAT and provides unblocked ports, including port 25. The cheapest plan starts at $8/month. Here's a link!
I wonder if I somehow can set up my Mikrotik routers to tunnel through you and transparently provide IPv6 for my whole LAN, that would be swell.
I never tested WireGuard, but, for instance, I had no issue connecting via OpenVPN to personal and work VPNs from China (on standard ports with no effort to hide). If you try and use OpenVPN to connect to any of the well-known VPN providers with it though, it will be blocked.
Even if you find it works initially, as soon as someone catches wind of it being used to bypass the firewall and/or they see a surge of traffic to your services, you're likely to end up blackholed.
Especially for a paid service, it's probably more of a support headache than it's worth.
Unless you're looking to make a stand, I'd probably just steer clear of the whole situation. It's illegal in China to operate an internet services without a license and it could come back to bite you in the ass down the road if you ever intend to do business there or travel there.