Using wp_register_style to load CSS in footer?

Technically styles should only be output in head and outputting them elsewhere is invalid HTML (browsers are however very lax about it and don’t care much).

So in best interest of standards WordPress wouldn’t do something like that. Right? Right!?

It does without bit of remorse actually. There is print_late_styles() function, running in footer that will output any queued styles that hadn’t appeared in the header.

So while there is no explicit way to enqueue style for footer (like for scripts), simply adding them into queue after header had passed will make them appear there.

Still not too good of an idea, but it does work.