FYI: The rationale for making them "child" plugins is this:
1. I don't need to use specific option checks to let someone turn on or off the components (such as the allow images; allow video).
(Having the Toolbar Images Panel plugin activated implies that the site wants to allow images in bbPress replies).
2. Turning off the defaults would be useful if competitive buttons were preferred, if Joe makes a superior Formatting selection of buttons, then others may prefer that.
3. Having the defaults as plugins may inspire others to make plugins that extend the toolbar.