WireGuard provides the foundation of a complete VPN service. It doesn't provide features such as user management and authentication, key management, ip address assignment, client configuration distribution, end-user friendly VPN clients, support for easily implementing complex split-routing and dns configurations for VPN end users. And most of those things aren't in progress. And it is likely there will be multiple solutions competing to provide these on top of WireGuard, so there may never be on true flavor WireGuard solution. Also once these are in place the overall attack surface expands to be closer to OpenVPN and IPsec.
Other issues include lack of support for multicast which means IPv6 which requires multicast is mostly supported but not completely which can cause issues in some circumstances.
Accomplishing some simple tasks like using a floating route to provide failover across two WireGuard links isn't possible. WireGuard interfaces don't go down unless you manually tear them down, so you either have to run another tunneling protocol over the WireGuard links and assign your routes to those interfaces which can go down or use a dynamic routing protocol. And WireGuard has a few caveats when being used with certain dynamic routing protocols which starts to make it as complicated as OpenVPN or IPsec at scale.
Currently there is an issue being discussed on the WireGuard mailing list regarding there currently being a requirement for time to be set on devices before establishing a first connection to a peer. This is because of an anti-replay requirement WireGuard has for initial packets which IPsec and OpenVPN don't. This is impacting a group that was hoping to use WireGuard to encrypt the traffic across a community wireless mesh network. The devices used in such networks often don't have a realtime clock. There are potential workarounds but again suddenly the simplicity advantage starts to slip away.
I think Jason has done great work, I like WireGuard and I use WireGuard, but it is not near ready to replace OpenVPN or IPsec in most circumstances.