Keeley adds this feature to the Ibanez AD9 with their mod. They add a true bypass on-off switch, then rewire the original footswitch to be a momentary switch that controls the regen/oscilation, like maxing out the repeat knob.
The Strymon Brigadier does this. You just step on the left footswitch for a bout a second, and the repeats take off...take your foot off the switch, and the oscillation ramps down again. It's cool, as you all have stated.
I've got the Keeley AD-9 and the oscillation feature is neat. I keep it on the front part of my board so that I can keep my heel on the ground while pressing the switch. This makes it easier to bend down and work the delay time knob while it's oscillating. I also will use it like a piano's sustain pedal which can be cool.