At the last event "PTC LiveWorx Europe 2015" in November of 2015 it was presented a roadmap for the development of Mathcad Prime 4.0 and some future steps (themes) for Prime direction. PDF "PTC Mathcad Roadmap_2015" can be found in attachment. You can see what updates are planned for version 4.0 (now the release of version 4.0 is scheduled for the 4th quarter of 2016 year) and is scheduled for subsequent releases after 4.0.
Update: New timeline (at time of June 2016) for Mathcad/Mathcad Prime product:
