So, I think WireGuard can't, but it can be used as a part of the puzzle. I'm running a mesh using WG as the security layer, and then l2tp to provide a layer 2 on which to run batman-adv. I have a bunch of machines getting DHCP addresses from my home router that way, and (I assume) batman gives me good routing. Of course, cobbling together your own "secure" mesh probably isn't ideal, but it works surprisingly well.