9 or 10 gears?
How big of a transmission are we talking about? If it is a FWD transaxle, there is much more limited space.
How big are each of the gear sets?
are they robust enough to not wear out or shed gear teeth after years of use?
How often is this thing going to hunt and peck for the right gear ratio, and how much time spent shifting between 9 or 10 gears?
How narrow is the engine's power band? That is the only major reason for many gear ratios. A wide power band, which the new DI & Turbocharged engines are supposed to have, should require LESS shifting, not more.
How many bands, hydraulic circuits, and moving parts are vulnerable to failure, and trashing the rest of the gearbox? How much is a 9 or 10 gear gearbox going to cost to replace, or have rebuilt?
My family has had all sorts of different brands of cars that have required transmission re-builds. Chrysler, Ford, GM, and Subaru. Hondas are known to have potentially delicate transmissions. CVTs from all brands have reliability issues and seem to have higher repair rates after warranty expiration than automatics or manuals.
I don't trust efforts to introduce more complexity, and more un-proven parts, when they have yet to prove definitively that the transmissions are rock solid.
What brand is known for transmissions that *DON'T* need repairs beyond the regular maintenance fluid change service, and are more than capable of coping with any driving style, and any amount of power than the engines put through it.