i don't care if my seat is wet. water doesn't damage them... so i just wipe off the saddle with the sleeve of my shirt (if it has stopped raining), or just hop on it while it's wet (if it still is raining). if it's still raining, a seat with a few drops on it isn't what is going to make me wet.
if you're concerned with biking in the rain, and you're trying to design something that'll "help," perhaps something that dries your rims while you ride, without slowing you down. with wet rims it takes a cycle or two to clear to have effective braking. can be considered dangerous, esp. if you're a noob. a dry rim just before the brake pads would provide a safer braking experience.