Client wants to extend L2 over Dark Fiber thoughts?

Hello,

I have a client that has an on-site server room which contains a small collapsed core of Catalyst 9500 and hyper-v cluster running Nexus 9300 as TOR.

The building next door to the customer is a large DC that has a direct fiber conduit running to the customers building. The customer purchased two fiber pairs to the Colo rack, and I am in the process of setting up DWDM equipment. The original plan was to migrate the VLANs used on the Nexus hyper-v and storage while fork lifting the entire server setup to colo, then simply routing between colo and on-site core (about 800 users). In the process were also getting another set of Catalyst 9500 at the colo as the second core for MACSEC purposes.

Long story short, last minute customer wants to span the VLANs across the dark fiber. The fiber itself is about 0.3 miles distance with no real latency. The customer is insisting with there three "network" guys on staff to do it. They want to have the hypothetical ability to provision local hyper-v cluster in the future to do hyper-v equivalent of VMotion, and other L2 adjacency requirements such as slowly migrating existing VLANs on site to brand newly routed VLANs at the colo.

We offered the client to do an ASR setup with OTV which we have had good experience with, we offered VXLAN BGP EVPN. Admittedly these are more complicated solutions then needed for a customer this size. The customer has other locations but there correctly setup as routed interfaces.

Anyway, I would like to hear peoples thoughts. Honestly, we are against this, but I like to hear opinions or options were missing.