The 9000 cassette is 1.8mm wider, or 39.4mm.
The dt hub graphic is a 11 speed to 'Classic Shimano 10 Speed' comparison. Not specifically a freehub built 'only' for a 10 speed cluster.
All 9/10 speed generic hubs (except maybe some specific 78xx/79xx or similiar ultegra wheelsets) have a hub spline that indeed does measure 35mm or thereabouts.
This is to cater for the possibility of using a 9 speed cluster on the freehub.
In the instance of a 9 speed cluster being used, no spacer is used. There is also no 'overhang' of the biggest cog over into the spokes area. The cluster is 36.5mm long, and fits perfectly onto the 35mm freehub. Spoke rubbing should not be an issue, as the biggest cog is not 'set back' towards the drive side spokes.http://sheldonbrown.com/cribsheet-spacing.html
In a 10 speed cluster, the cluster is actually 37.2mm long, however it has the 'overhang' of the biggest cog over into the spoke area. How long is this overhang? Well, pretty much every wheelset with the common 8/9/10 speed freehub length of 35mm requires (on almost all hubsets bar a few with more inboard spoke ends, or touch shorter freehub bodies) a 1mm spacer, this takes the cluster length to 38.2mm.
So 'if' the clusters overall inner dimensions needed to put the lockring in the same place, and do up the same way, at the same distance to the freehub is the same between the 9 speed configuration, and the 10 speed with 1mm spacer, the overhang can be calculated at 1.7mm, by assuming the non overhang length is the same as a 9 speed cluster of 36.5mm, and allows use of biggest sprocket without the derailleur without spoke touch. (38.2-1.7=36.5mm)
Now lets take a 11 speed cluster. Reportedly the cogs are 1.6mm, the same as 10 speed cogs. The spacer between cogs is 2.18mm (via shimano tech docs). This gives a cluster width of 39.4 (which i've noted elsewhere as being accurate, but can't find the link :/ ).
If the overhang is theoretically identical to a 10 speed cassette i.e. 2.7 without a spacer, and 1.7 with, then the possible 'inside dimensions that are the same as a 9 speed cluster' are either
Obviously 37.7 is +1.2mm on the desired 36.5mm '9 speed dimension'.
But, the first one, without the spacer is 36.7mm, and is only 0.2mm more...
The real question then becomes which biggest cog, with associated 9000 rear derailleaur, is required to avoid the rear derailleur hitting the drive side spokes.
I'd love to try a 11-25 or 11-28, but I reckon 11-23 will definately not work, and 11-25 probably won't either. But 11-28... now there is a possibility that the combination of b tension screw, chainlength taking up alot of the derailleurs slack, and distance of the radius of a 28 tooth cog from the centre of hub, could effectively put it out of reach of the driveside spokes by the derailleur...
But how about instead of using no spacer, or a 1mm spacer, we try a .5mm spacer?
Maybe that gets 11-28 working perfectly, and maybe 11-25 as well? Puts the small cog approximately .7mm closer to the seatstay, but maybe that is still within tolerances?
Anyone here planning to upgrade their 2012 rear zipp wheel? Might be worth a shot to avoid a costly conversion.
Anyway, of course there are lots of assumptions in the above theory, most of which are spot on I believe. However, maybe it will work? Never know