Here is an interesting new product. Called Retroshift. It is a brake lever with a shifter mount on the upper part of the blade. Downtube or bar end shifters mount there, friction or indexing. It turns out to be a very natural shifting motion when you're riding on the hoods. Doesn't work from the drops unless you have freaky long fingers.
Pic on my bike, those are Simplex friction shifters and this 30 y/o Peugeot can now be shifted from the bars.
I've no connection other than paying them $119.