Summary: Like turning the Repository into the iTunes store. Devs can release plugins and themes for free or for $1 or for $10.
1) Developer makes a plugin
2) Developer (kindly) releases into WP repository for free
3) Developer includes a "Donate" button inside the plugin's administration
4) No/Few donations - apparently not enough to keep up with development or support
5) Plugin abandoned, but current and potential users don't really figure that out until after a year of no one ever hearing back from the developer or after realizing it is no longer compatible.
6) Repository is littered with plugins that aren't compatible with the latest WordPress (I know, some people don't upgrade - maybe for the reason that they just HAVE TO HAVE that plugin) and/or aren't supported (not even by the community).
1) Make plugin
2) Release in repository, set price of $1
3) Can still include "Donate More" button
4) Every download charges me automatically $1. Developer doesn't get my contact information (unless I want them to), doesn't feel as compelled (maybe) to include a "Donate" button everywhere all over the plugin, and is much more likely to continue supporting a plugin that has 20,000 downloads. Also helps not to have to maintain a Lite and Premium version - but they could if they still wanted to.
5) Plugin not abandoned by the community or the developer/support.
6) Repository is of higher quality if less plugins are abandoned. (And incentive for more developers to release.)
A) If plugin becomes abandoned or incompatible with latest version of WordPress, it automatically becomes free.
B) Pay each time to download to a different install? I don't see why not if it's only $1.
C) Or, you could just attach the WordPress Extend "Market" to our WordPress.com logins, as long as we have our blogs setup in there (like JetPack or WP.com Stats).
D) All updates mandatory no charge (just like iTunes store) - keeps things working nicely together and encourages updating to the newest release of WordPress.