I run friction shifting on 9s, and find it works well... perhaps easier to shift than the original 5x2.

My config is actually vintage Campy shift levers (the bumpy ones), with an Ultegra 6500 (I think) Rear Derailleur. I get essentially full tube to tube range with my right gear shift lever to shift the entire cassette.

It doesn't make any sense to discuss speed specific friction shifters.

It looks like the new Shimano derailleurs take less cable pull than the old ones, thus less lever movement to shift. Good for some setups, not so good for others.

So, for example, I'm maxed out on lever range, so I could not use an 11s cassette with my current setup. But, it might work with a Shimano 6800 rear derailleur (or any Campy rear derailleur).

https://en.wikibooks.org/wiki/Bicycl...ing_Dimensions