I'm unsure as to whether or not this has been suggested previously or not, a search provided no relevant results so apologies if this is a duplicate.
The other day I found myself looking for a membership paid subscription plugin and it took a considerably long time to track one down. Eventually I found the ideal plugin but it wasn't in the usual WP repository. It's a paid plugin (I won't mention which one, I don't want this to look like I'm promoting a particular plugin) and the only way I could find it was via a web search.
My suggestion is to have a separate plugin repository specifically for paid plugins in order to make them as easy to find as the ones located within the standard repository. There could even be a small monthly fee for each plugin within the paid repository, after all these are commercial products and WP would effectively be promoting them (albeit in a small way) so a monetary kick back would be good to put back into the development of WP itself.
Now, I'm unsure if this fits with the WP philosophy (I'm waiting for somebody to shoot this idea down) but I feel that purely for the convenience of those who want to invest in their sites/blogs by paying for specific pieces of perhaps more advanced functionality not already available as a free to use plugin there's no reason to stop them and also add to the company's own revenues.
Thanks for the consideration.