TYPO3 Core

Also #17568 is related - it's mentioned, that it will be in the 4.2 Core - but not how exactly.

#17568 implements a hook to display something else than "CODE:..." in the columns view of the Page module. That issue not about the way the different fields are displayed when editing a content element.
See discussion in Core list: http://lists.typo3.org/pipermail/typo3-team-core/2007-August/008872.html

I'd position it right below the 'list_type' field - just above the flexform.

Currently, if you add a plugin, you need to switch to the "Plugin" tab, select the plugin, switch to "Behaviour" and change the select_key. If you use a flexform enabled plugin, you don't need to switch to the behaviour tab - it's all right there.

Since the pi_flexform somewhat replaces select_key, it seems to be obvious that both are located on the same spot.