Have encountered edge fabrics that use leaf-and-spine with VXLAN/EVPN? For DC fabric we used leaf and spine, but for the edge fabrics (branches, internet, 3rd party connection, and cloud direct connect) leafs will connect to CE-routers.
On our old DC edge fabric traditionally uses core-dist, but the old DC is not multi-tenant. The edge fabric and DC fabric then will be connected through border leafs, so the DC fabric border meets border edge.
Yes, I’ve seen people using VXLAN in WAN, either with static ingress replication or EVPN. You can also use EVPN with MPLS transport.
People are also extending L2 networks between data centers with VXLAN/EVPN (not necessarily a good idea, but let’s not go there). If you want to do that then it doesn’t hurt if your switches can do VXLAN-to-VXLAN bridging.
Finally, EVPN is probably mature enough to use as a pure L3VPN solution (I would run some tests first), so you could use it to build WAN multitenancy. However, you might have to figure out how to go from L2+L3 EVPN in the data center to L3-only WAN EVPN. Never tried to set that up.