Something like that has been tried before, using a timer display. It was pretty disastrous because people accelerated to beat the red. I think this was in China, so perhaps in other countries it might work better if the driving culture was more cautious.

Timers on the red seem to work well though, giving people advance waning to prepare to go, get in gear etc. There is one near me that seems to help get the traffic moving through faster when the lights change.

Blinking yellow already indicates proceed with caution in the US, so this would lead to ambiguity, which isn't something you want on the road.

No, you need a blinking green that indicates it's about to turn yellow! And this already exists in some countries.