When you use a collaborative playlist (private or public) for a certain event and you do not want to be spammed with songs by a single contributor, because he likes to hear a loooot of "his" music, it would be nice to have a feature, where you can set the maximum songs that a user can add to the playlist (global playlist setting, not for each user). If a user wants to replace one song for another one he should be allowed to do so within the specified limit. This makes sure, that everyone gets to hear his selection within a reasonable timeframe. Further more the playlist should be lockable without having to throw out everyone in order to keep it consistent during or up to the event. For example: When preparing a party, everyone who is invited may contribute to the party playlist and it is locked with the party starting, until everything was played (manual setting for the creator, no automation needed....that would be nice, but overkill for now). Then he reopens the playlist again, also unlocking the limit to give people the choice for further selection of titles for the rest of the night.