I think Rack extensions SDK should be downloaded freely to allow programmers time to learn and develop rack extensions.
Then when a rack extension was completed I agree filtering by Propellerhead before publishing to preserve quality and reliability.
Actually there is no information about how can be programmed (C++, Objective-C,?), there are no examples, ...
Now Propellerhead filtering is absolute just from the beginning, and access to SDK, documentation, examples,... is forbidden. I think Propellerhead should give free access to SDK, documentation, examples,... and filtering should be made just at the momemt to publish rack extension. Maybe this can contribute to expand rack extensions gallery.