BuddyPress.org

fyi, most developers include donate links with their plugin. Either on the developers website or in the plugin readme or the plugin download page. This way you can choose which plugin to support or to create incentive for the developer to prioritize a feature.

I guess also, don’t wait for a system, if you feel a plugin is deserving the time and effort put in, just support it. In reality it might give the developer a chance to buy a starbucks coffee, since my limited experience tells me that donation are far and in between. Thanks for bringing up the fact that developers should be encouraged though!