For ProtonVPN. Same company. Statement made on the assumption that resources spend on ProtonMail can be spend on ProtonVPN (which I admit is a stretch).
Given how simple WireGuard is to set up I don't understand why they don't support it. Their UI etc, sure. Then just make it alpha or beta or whatever. I'd happily test it. Give feedback, etc.
Meanwhile, I paid for a 2 year sub and barely use it because of this reason. Instead, I run a WireGuard VPN _to_ my home cable connection.