I could be wrong, but my feeling is that the reason versioning keeps getting singled out in this thread is because it is the only service in my list above that is intrusive in its implementation. In other words it's the only service which affects the way you design the datamodel for your content.
As Stephen points out, for all the other services, choosing not to use a service geared for the CR has no particular overhead. They could also be equally well applied to acs_objects as cr_items.
_If_ (big if) versioning was implemented as a transaction log external to the contents own datamodel, would there still be a problem with allowing acs_objects to be versioned?
If not, I think OACS would benefit from having its base object type have direct access to those services needed by site content. For example if the bboards also arranged their posts in folders, administration staff who might author content using a folder based interface could also moderate from the same inteface. If that were suggested with the current CR I think the main objection be that the posts would then have to have the versioning overhead.
