Finally someone inside Microsoft has given us a first response on this topic: what's the roadmap about developer's certifications now that .NET 3.0 is alive?
Tha main facts are these:
- They will plan to release between 2-3 Technology Specialist exams (each exam will yield a TS credential).
- They will not plan to change the professional level exams at this time (good).
The new Microsoft certification's stragey is clear: "you're never "upgrading" your TS credentials, just achieving new ones". A great choice... 
Regarding the idea to group WF with WCF in one exam, I can't agree. Windows Workflow will be a new technology that is "cross-sectional" between Winforms and WCF, so I think that the best choice will be to release a single standalone exam for WF.