Suggestion: Additional posting & visibility options for groups

I would really appreciate the following additional options for posts in group sections:

• Unlimited change time
  Most of the group contents are not "blog discussion" which require meticulous archiving but content collections where mistakes might be discovered months after the publication. 
• "Invisible" posts & changes
  Some posts are not relevant to appear in the main Conversation section - they are just supplemental. For example it hurts that each time I add a CSV-list to goulnik's excellent tables this bombs into the main conversation lists. It is a minor add-on not something worthy to be made that public. 
• Open posts, wiki style
  There are some posts where I would like encourage each group member to add corrections or additions.
  Design options: With or without highlighting of changes. With or without history.