In some cases it makes sense to use esi/ssi for some panes on a page, but ajax for other panes on the same page. It would be great if the setting for this were tied to the specific pane and not globally.

Comments

From a technical standpoint this is easy to do. Inside of theme_esi_tag have the $data variable contain mode; default to variable_get('esi_mode', ESI_MODE); if not set.