This would extend the usability for a public kiosk that doesn't have a physical keyboard. In "kiosk mode" toolbars, control panels, and basically the whole user environment is locked down for security purposes, so the virtual keyboard needs to be activated by some other way. Perhaps automatically popping up when a user text field is selected. Most kiosks use browser technology, so perhaps this could be initiated via a mozilla plug-in. If that proves too difficult, an always-on-top icon could open and close the keyboard as needed. The bottom line is that, being a public use tool, usage must be intuitively obvious, even if that requires dumbing it down slightly while in "kiosk mode".
Note that this would be a boon for kiosks because virtual keyboards are much more robust (no moving parts) and secure (thwart keyloggers, etc) than physical keyboards.
There is now the option to make a floating icon appear when onboard is hidden. Clicking on that icon makes onboard reappear.