Funnily enough, they've just released an update! Yes, I was taken by surprise a bit.

EdgeRouter 3.0.0 [1] adds official wireguard support (I've been using the "wireguard-vyatta-ubnt" package from Github [2]), UI changes and some other improvements/fixes. I haven't tried it yet but will. I have an Edgerouter3-lite and an ER-X.

[1] https://community.ui.com/releases/EdgeRouter-3-0-0/33ee3852-...

[2] https://github.com/WireGuard/wireguard-vyatta-ubnt