I had… a Restaurant theme. 
4 yars ago.
It stopped at an early stage (not for technical problem but for a personal problem of one of us, we were three and one guy left the project).
Every feature was developed as plugin but then merged to the theme (dishes, opening times, online booking).
That decision came from the marketplace choice… we choosed to sell on envato and so bundling everything in the plugin was the only viable way.
I think that this statement have to be deeply considered on the directory developement. And could add a great value!