There's no need to remove motorized infantry from the building queue, neither to add a truck brigade...
All we need is, pretty much like HJV said, the ability to change ordinary infantry divisions to motorized ones. And from motorized, perhaps to even mechanized. That would be historically accurate, and make things less silly...
The British army, for instance: in '39 scenario their army is completely leg
infantry.
In Awakening the Giant, some of those divisions are suddenly motorized, some aren't.
In '44, they're ALL motorized infantry.
This represents the transformation of the army from foot/horse drawn to truck/halftrack-based, the divisions have same names (50th Higlanders are 50th Highlanders in 1939 as Infantry and in 1944 as Motorized Infantry) and with respective experience, all good, but when actually PLAYED through those years this just can't be done!
Another good example is the 5th Waffen-SS, Wiking. When building Motorized Infantry, that name pops up. Of course, it was formed as such. But if you build Mechanized Infantry, you come up with ANOTHER Wiking! Yes, true, in '43 Wiking was reformed to be the 5th W-SS Panzergrenadierdivision. And then, with armoured divisions... you guessed it! In late '44 Wiking was indeed given a whole armoured regiment, and it was named as the 5th SS-Panzerdivision.
I have had all three Wikings in the same battle, and it made me to beat my head to the keyboard in powerless frustration. Changing names felt like cheating.
Just keep it possible to
1.Build infantry Divisions,
2.Build Cavalry Divisions,
3.Build Motorized Divisions,
4.Build Mechanized Divisions,
bul for the unexistingdeity's sake MAKE IT POSSIBLE to
5.Upgrade Infantry Divisions to Motorized Divisions,
6.Upgrade Infantry Divisions to Mechanized Divisions,
7.Upgrade Motorized Divisions to Mechanized Divisions,
8.Cavalry Divisions to Motorized Divisions (I truly can't understand why on Earth isn't this featured in the game already!)
9.Cavalry Divisions to Mechanized Divisions
and perhaps even Motorized and Mechanized (or only the Mec) Divisions to Armoured Divisions.
This would allow things go smoothly, intelligently and historically accurately. Divisions would keep their experience and names, and use less time in upgrading than disbanding+building from scratch needs.