A question that will likely come (has already come) is how many service meshes can be federated together. Some customers will have quite a large number of meshes, which could result in a very large number of federation pairs. While service mesh federation is not intended to cover federating a very large number of meshes (a multi-cluster service mesh - future for OSSM), customers still want to know limitations. 

We may not be able to publish hard numbers of limits, though we can add a paragraph discussing considerations when federating multiple meshes. rcernich1 commented - "
Scaling will largely depend on the number of services exported between meshes, which is what drives network traffic between the meshes for discovery.  Size of the local mesh may also be a factor, as the export logic will scan the entire service registry (larger registry, longer scanning time), but this is pretty normal for the mesh.". Perhaps this can be expanded upon. 
 
This issue does not gate the 2.1 release, though we should look to include it the moment the question comes up post release.

Outcome: small/medium/large meshes and approach to scoping doc