CVT incorporated in a hub motor would result in a huge drive system, not only in physical dimensions but also in cost.
Geared hubs such as the 3,7,8 and 11 spd Nexus/Alfine have proved to be perfectly capable of handling the combined effort of both rider and center-drive motor for many years now....there are thousands of them in use in many countries of the world.
Recently on this forum, I have seen several unsubstantiated claims that center drives are causing premature failure of Shimano geared hubs....documented evidence please!.
And of course, Shimano do not recommend that their geared hubs should be subjected to the dual forces of both rider and center electric drives, but since when, in the unlikely premature failure of a geared hub is the consumer left to fight it out with Shimano to get a replacement under warrantee. The answer is, they don't, the manufacturer of the machine will replace the geared hub without question. It was after all their decision to use it.
Road gearing on electrically assisted bikes is always a problem, the worst offenders being those machines with batteries behind the seat-tube, usually eliminating the use of double or triple chain-rings. If you really need such a huge range of ratios on an e-bike, then there are currently available several options....and the prohibitively expensive and overly heavy Nuvinci CVT is not one of them, at least not in my book.
For the past three months, I have been riding a Bosch powered machine. The Bosch drive is very narrow-gutted....the distance between the crank-arms little more than that of a normal road bike with a compact gear-set. Obviously, there is not room for even a double chain-ring. Nevertheless, the machine has a very wide gear-inch range by the use of the SRAM 9/27 Dual-Drive. The concept of the Dual-Drive is of course very simple, instead of a triple chain-ring, a 9 spd cluster is grafted onto a 3 spd geared hub.
The geared hub component of the SRAM Dual-Drive has three positions:
'Uphill' (underdrive) provides very low ratios, in 1st gear it would probably be quicker to get off and walk (and take the opportunity to 'spark one up' and restore the nico levels). lol.
'Flat-ground' (direct drive) taking full advantage of the high efficiency of the derailleur component. In use, top gear (18th) is nicely matched to the maximum assisted road speed of 16-17 mph at a comfortable 60 rpm cadence.
'Down-hill' (over-drive), I've only tried this on a couple of occasions. In 27th gear (128 gear-inches) with a good stiff tail-wind, I managed 25mph at a steady 60 rpm cadence... the electrical assistance having left me to it long before I reached that speed....a very 'tall' gear indeed. I'd even go so far as to say I prefer the SRAM Dual-Drive to the 8 spd Alfine geared hub fitted to my Kalkhoff Sahel Pro Disc.
In summary, If you really need so many gears on an electrically assisted bicycle, there are far more efficient and less expensive ways of doing it than CVT's in hub-motors or belt driven Nuvinci geared hubs, the latter being the territory of the money-no-object fashionistas.
Regarding the Cyclotricity machines, the triple chain ring is an unnecessary complication as regards setting up and maintenace. Providing the machine is fitted with a minimum 9ah battery, the motor is powerful enough to cope with all but the steepest of hills and heaviest riders.
