Isn't Eclipse Marketplace just aimed at providing a location to install features into a running p2-aware Eclipse application from? This is different from developers needing a way of getting binary artifacts (.jars) into their workspace (using Maven, Buckminster, Gradle, or your favourite build tool).
In addition to providing components that have been IP checked to a certain standard, Orbit also:
* provides a stable set of p2 sites
* for packages where the upstream provider has not included OSGI bundle information, Orbit provides a repackaged jar with the required OSGI headers in the manifest, so it can be published on the Orbit p2 site
These benefits are incredibly useful. There have been multiple attempts to provide such a resource (minus the IP checks). Examples:
(1) SpringSource Enterprise Bundle Repository
http://ebr.springsource.com/repository/app/" Here you'll find OSGi-ready versions of hundreds of open source enterprise libraries that are commonly used when developing Spring applications"
No longer maintained
FWIW
Matthew