Before they went Retina, iMacs could be used as displays in Target Display Mode. Is this possible with the new Touch Bar / USB-C MacBook Pros (late 2016) via the USB-C ports? They don't have a Mini DisplayPort-style Thunderbolt 1-2 port, and the support article about connecting various things to the USB-C ports doesn't mention an iMac. Neither does the article that explains what can and can't be used with the USB-C to Thunderbolt 2 adapter.
Don't confuse a USB-C / Thunderbolt 3 port with USB only as the new MacBook Pro do have thunderbolt and not simply USB-C. The new MacBook Pro can output to a Mini DisplayPort target display mode compatible Mac with either a cable that connects directly or an adapter to the existing cable you would have used with the Mac.
I would probably go with a USB-C to MiniDisplayport and use the display port over USB-C protocol since that cable is less expensive than a thunderbolt adapter and would also work with a MacBook (non Pro and non Thunderbolt) or other USB only device. There's probably no speed benefit of thunderbolt for this application.
If you wanted thunderbolt - then you'd get Apple's Thunderbolt 3 to Thunderbolt 2 adapter - $30 on sale this month and use any standard thunderbolt cable. I used to believe all iMacs that support Target Display mode will take mini display port signal in - but some people report you need thunderbolt for some Macs. I have no reason to doubt them - so be sure you can return a DP cable if you buy one for this. Some iMacs support both thunderbolt as well as mini DP. Not all iMacs with either port support Target Display mode - especially the new 4k and 5k iMacs - they don't support any video input so you would need a software screen sharing solution for them.
- https://support.apple.com/en-us/HT204592 - Use your iMac as a display with Target Display Mode
Yes, I have connected my Late 2016 Macbook Pro using a USB-C to Thunderbolt 2 adapter (from Apple) to my Late 2012 27" iMac using a Thunderbolt cable (from Apple). Target Display Mode works the same as with my previous MacBook Pro (Late 2013).
The only issue so far is that the volume slider won't appear on my Touchbar for controlling the iMac's volume.