Originally Posted by Leinster

Cable pull =/= cassette spacing.

You can use campagnolo, SRAM and Shimano 11-speed cassettes and chains interchangeably because the spacing between the sprockets in the same, so the rear derailleur moves the chain the same distance left-to-right-to-left-again for each shift.

However the cable pull ratios are different on all 3, so when you click a campagnolo shifter, it will pull a different amount of cable to what a shimano shifter will for the same click. This means that a Campag shifter connected to a Shimano derailleur (or vice versa) will not travel the right distance from right-to-left to get you from the 11 to the 32 and all points between (others here will be able to tell you if it will leave you short or overshot, but basically it won't get you there).

You can still use a Campag RD up to 34t, and if you want to go bigger at the back you can look into a Wolftooth Roadlink as others have mentioned.