I have friction shifting of 9s on my old Colnago.
Vintage Campagnolo NR downtube shifters X Shimano Ultegra (6500?) rear derailleur.
It works very well, and shifts better than 5s or 6s ever did. However, with the pull, it does essentially full tube to tube movements of the shifter for the rear.
I also have tried 11s friction shifting on my Jamis.
11s MTB XTR Rear Derailleur.
Tried vintage Suntour and Shimano bar-end shifters. The Suntour shifters don't have enough range of movement. I will probably try to modify the shifters for greater range of motion.
The Shimano shifters do have adequate pull, but they aren't designed for the full range of motion. They will barely work, but on the high end (small sprocket), one has to over-shift them, and there is too much spring tension, and the derailleur tends to pop back. I think the opposite was true at the low range (large sprocket). Not enough tension in the shifters, and too much in the derailleur, and it still didn't hold.
Overall, thoiugh, for the mid-range gears, it worked very nicely.
Note, the 11s Shimano MTB has a lot more cable pull than other Shimano shifters, so more space between gears.