Can the WCF Service(CKSDev) be used to build  a .net framwork 4.0 WCF Data Service to be deployed to sharepoint?  Can this even be done at all (i.e. without cksdev)? Can the frameworks really run side-by-side?

I want to use it in a BCS Model

Since it's a general question, I'd suggest you try to post it at http://mssharepointforums.com.