Conceptually if you just put a 2 speed in series with a 5 speed you will have a 10 speed. You could cut multiple gears into a single forging and spin the whole thing with just 2 bearings. Or you could could modify the design of a Pelton wheel so it has multiple rings of cups on the side of a disk and run the output through a high ratio reduction gear. Put cups on the other side facing the other direction will give you a range of gears in revers as well.

It is called a split differential Slowburn, usually very heavy, also ZF gear boxes Chris are designated 4hp, 5hp 6 hp not HP 9 it would be a 9HP then another number to reflect how much horse power it can withstand, hence 5HP-19 or 5HP-24

Why waste money designing and building a new design of gearbox when there are already perfectly good ones available, at good prices, made by gearbox specialists?
The answer: So that you can say it is made in America and get all xenophobic about foreign products.This is ridiculous nationalism at its best, not to mention reinventing the wheel.
More gears is not a measure of how good a gearbox is in terms of efficiency or feel. I bet the ZF gearbox's will still be better because they are made by gearbox experts and not ordinary car manufacturers. Ford and GM would be better off spending their money on improving quality control measures for the vehicles they currently make instead.

5 gears, 6, 7, 8, 9, ... geezuz chrysti, can you just quit with the more gears b.s. and go CVT like you really want to. What's the point? Your 25 gear transmission still will be no match for CVT, so quit creeping up to the finish line and just stand up and run over it already.

I'm with PDB. Instead of putting all this money into 9- and 10-speed transmissions, why not spend the same or even less on CVT? After all, CVTs are already in some cars, and you have NuVinci already trying hard to get solidly in the market. Surely there are other suitable designs, too.

re; PimplyDykBallz
CTVs suffer from high internal friction and corresponding wear rates, and slip under high torque loads.

re; Oztechi
Do you really think that Ford and GM don't have their own gear box experts?
There is also cost Ford and GM don't need to make a profit on gear boxes so they will get The ones they build themselves at cost. Maybe they want their new transmissions to be compatible with engines that have already been built.
Experts aren't always right.
Maybe they want their new transmissions to be lubricated with the same Glycerol antifreeze solution that they are going to be using in their engines. (Unlikely but stranger things have happened.)

QFT. CVTs cannot yet take the power of a transmission with conventional gearsets. They work with smaller cars, but with more powerful cars, they simply do not hold up.

@Slowburn, take a look at Torotrak. They make a CVT , and I think they were before NuVinci. There are no belts to wear out. Their system also includes KERS.

Ah the last gasps of a dying tech. At best this will increase fuel eff by 2-3%. So they increase eff from 7 to 7.2%, big whop!!
But eliminating it, the engine and replacing it with a many x's more eff E motor increases eff 200-600%!
My lightweight EV's get 250 and 500mpg equivalents and only cost 25% of a gas version to run.
Tesla sent them the memo but I guess they didn't read it.