Well this is interesting and came out to be a great discussion in one of our presentations with the client. Express Route can be enabled with Microsoft Dynamics CRM online.
Well this is indeed a great news as you can create private connections between Azure datacenters and infrastructure in your environment.
More details you can go through this article:
https://community.dynamics.com/b/msftdynamicsblog/archive/2015/12/01/announcing-support-for-azure-express-route-for-crm-online