Hmmm . . . unless I'm misunderstanding your question, the Yamaha MagicStomp II does that now. You have two basic modes of operation: the three foot-switches can be mode-up/on-off/mode-down, or assign your three favorite effects, and the buttons become effect-1/effect-2/effect-3 on/off.
It's a cool pedal.
Out of production, I think. But still available on the bay and such.