If a friction shifter can pull enough cable it can shift anything. But an 11 speed cassette will have closely spaced cogs and may be a bit finicky to friction shift smoothly.

Having said that, I'm such a cheapskate I'm going to test run a mish-mash of Dura Ace 8-speed and 10-speed components by using a bar-end shifter cannibalized from a time trial bike's aero bars, possibly in friction mode. I haven't decided yet whether I'll like the carbon fiber frame I'm building up -- I won't know whether it fits until I ride it awhile, since it appears to be a 58cm, right on the verge of being too big for me. So rather than commit to buying pricey brifters I'm gonna hodge-podge it together for now.

I'm expecting it to be finicky in friction mode with 10 cogs. I've been running my 7-speed Ironman with friction shifters for a couple of weeks and it's a chore to shift smoothly on chipseal and rough pavement. Some of my favorite rural routes are so torn up it's like riding on bricks or cobbles, and I've blown a lot of shifts with a 7-speed setup and downtube friction shifters.

BTW, Sheldon Brown's site has quickie compatibility charts for Dura Ace components. I dunno if he has another page for all Shimano, Suntour, etc., but it's worth browsing his site to find out.