Here is the roadmap they showed at MEDC 06:
And this is the info from the TechDays Windows Mobile roadmap presentation which they gave to all WM developers:
“Photon” (Q4 ‘07)
New, Flexible Shell
Modular Containers
“Yamazaki” CE kernel
Q1/Q2 ’08 Marketing Launch
“Crossbow” (Q4 ‘06)
Great mobile messaging
Advanced Business and Enterprise propositions
Strengthened phone experience
Faster, easier application development and distribution
Q1/Q2 ‘07 Marketing Launch
So really WM5 SE is more of a business/phone upgrade and judging from the TechDays Developing for Windows Mobile presentation (no product demo's sadly) should make it a better platform for .NET developers.
**EDIT**
Here is the release roadmap from TechDays: