I think if in plugins would be "to do" section (after screenshots or stats) would be great.
Make it like "support" button: for each "to do" it could create Topic. In that topic plugin author describse what will be created/added/updated in future version.
Why use topics: so that regular users could add their suggestions on plugin, like: "create some feeld for more easy settings" and if plugin author desides to do that thing he presses the "add to "to do" list" and enyone will know that this is what is planing to do)))
Or if in "support" the topics could be created somewere alse then "problems and truble shooting" and in "support" topics with mark "suggestions" would be a chance to "add to "to do" list" (and "to do" page would look like list of anchors to "support" topics and may be simple text (that can be added from readme.txt in plugin).
haven't thought about it realy seriosly: how and why that and that..
But the idea i think is good!))
PS: sorry for my english, it's not my native)