Synapse will be hosted at matrix.matrix.wmflabs.org but just matrix.wmflabs.org would be a nicer username postfix. There are two ways to achieve that:

• serve a https://matrix.wmflabs.org/.well-known/matrix/server file, with Content-Type: application/json and Access-Control-Allow-Origin: * headers, with the content { "m.server": "matrix.matrix.wmflabs.org" } (alternatively, just redirect https://matrix.wmflabs.org/.well-known/matrix to https://matrix.matrix.wmflabs.org/.well-known/matrix
• create an SRV record at _matrix._tcp.matrix.wmflabs.org. with the value 10 0 8448 matrix.matrix.wmflabs.org

For more details see here.

Neither option seems available for the project admin so I would appreciate help with it. The preferable approach would be redirecting https://matrix.wmflabs.org/.well-known/matrix (or maybe just a CNAME from matrix.matrix.wmflabs.org to matrix.wmflabs.org if that doesn't mess up things too much) from my perspective, as that's useful for other things as well (e.g. a not absolutely necessary but useful thing to do would be serving https://matrix.wmflabs.org/.well-known/matrix/client).