Swobo used to have a seatpost with an integrated blinky. Good design,but you had to have at least a certain amount of post sticking out. Same issue I see with this Kickstarter deal,although it would prolly work pretty good for mini velos and folders.

Bianchi used to have a seat with integrated lights,but they were pretty dim and the weird flashing pattern wasn't effective. I always thought that if they'd just used some proper output red LED's with a regular blink pattern they would've had a neat item.