Talbot All Road.

Hope sell "11-speed" (road) freehubs that fit the Pro4 hubs and the Pro 2 Evo 40T but not the non-40T Pro 2 Evo or earlier.

The Hope 11s freehub has an extra pocket at the hub end of each splinegap.

http://www.hopetech.com/11-speed-compatibility/

Yea. I've got a Pro 2 evo with an 11 speed freehub on it that requires a little spacer for ten speed shiz. And 11 speed MTB shiz presumably.

Maybe Shimano will silently make the factory MTB wheelbuilds 11 speed road compatible like Mavic do. Who knows.

MTB spacing is the same as road for 11 speed?

As far as I know the gap between the sprockets is the same, but Shimano made the curious decision to make their 11 speed MTB cassettes fit the old 9/10 speed freehubs - which results in the unpleasant consequence of contemporary Shimano factory MTB wheelsets unable to take 11 speed road cassettes as they use the old 10 speed freehub design.

Interesting. I'm using an XX1 cassette on the CAAD12 but with an XTR mech. Wondered if I could swap back and forth with other wheels.

Assuming you want to put a ten speed free hub with an 11 speed cassette on the CAAD12, a shimano 11 speed mtb cassette is the answer, as long as you don't mind large sprockets.

will an XT/XTR Di2 rear mech work with road 11-36 cassette then?

I've never tried it, but I don't see why not, assuming your 11-36 is eleven speed. But then you'd just buy the 11-36 MTB cassette and save yourself the worry.

Surly Zinn has done a chart or something that explains all this stuff.

I could quite happily run an 11-36 cassette on a 27.5 MTB wheel set on the Time Machine. Hmm.

Should do, and the sweep angle of the cage shouldn't be that far off. Better than road mech with MTB cassette at least.

11-lessthan40 is hard to find in 11s MTB.

with 1x and no chain catcher I am in constant fear of chain drop .. might just get the XT Di2 rear mech, sorry for de-rail.

Narrow wide chainring?

Which is kinda bonkers given they do 2X11 groups.

So basically, this is a huge minefeild, and I'm just going to completely avoid factory wheels altogether and get set of identical hubs built up onto whatever rims fit the bill.

Yes.

Why? I've ridden down stairs on bike with 6870 derailleur and NW 1x ring and I've yet to drop a chain.

Bitex are cheap enough that this is completely viable. Shop in brighton does them for ~£130 a pair I think, crc 650b i21s are £25 each. Easy sub 200 wheelset