Make sure everything that is available from the SOAP api is available from CSOM
Currently you cannot get some things from the CSOM/REST api that you can get from the SOAP API.
For SharePoint Lists - Getting the AnonymousPermMask property requires the Lists.asmx soap web service.
For SharePoint Sites - Getting the NoIndex, AnonymousViewListItems, and AllowAnonymousAccess property requires the Sites.asmx soap web service.
Listing all site collections in a web app also requires SOAP.
We definitely need to go through everything in the SOAP API and make sure that all still-relevant properties and operations can be done with CSOM/REST.