Use a default and extendable design for post type activities

[imath]

In #8052 we've improved the way new_blog_post activities are output into the activity stream.

According to @teeboy4real BuddyPress is expected to provide a guideline or filter for uniform design styling to activities created from custom post types.

I agree we should make it possible to have a uniform design, my question is should it be the default behavior or should Plugins "opt-in" to use it?