Okay I am a lurker on many iPhone forums but never really registered for any unless registering was required for viewing. There seems to be a common misconception that Installer is going to 'be better than' or 'replace' Cydia.
Installer and Cydia are essetially the same application the only major differences being that Cydia is open-source and a port of apt which is a package distribution utility for Unix based systems.
When Installer is released applications are not going to magically port themselves to firmware 2.0. What is availible in Cydia is going to be whats availible in Installer 4 upon release.