ORIGINAL: loki100
I'd suggest a good compromise is lower cv and some sort of MP malus. In the end these are not trained motorised infantry formations and presumably are using a mix of vehicles, so they really shouldn't be as good as specialists in the role?
From my experience with this, I would say that CV is not the main factor here. There are some circumstances where you might want to motorize a high CV unit, but there are also others where you are using motorization as a kamikaze weapon, where you would actually prefer to suicide-run with low quality cheap troops than with expensive ones. That is especially true for the Soviets in the first few turns, though it may also be somewhat the case later in the game for either side, potentially. If Germany has made an early game pocket with a little whole in it, and you want to break the pocket but need to motorize to get a few more MP to do it, you don't really want to send a high quality unit into the pocket. You want to send a low quality unit into the pocket, because you don't want to lose an additional unit. You also want to send a unit with less trucks, so that if that sacrificial unit gets encircled the next turn rather than routed, Germany will capture less trucks.
The best unit for that job is something like an understrength unready NKVD border guards unit, which only requires ~50 trucks to motorize and may have 50-100 men. I have had good results with those units, and also with motorizing e.g. unready understrength paratroopers with 400-600 men. They don't do any fighting, but they flip hexes, and that can easily be all you need to either open a pocket or to cut off supply for all the German Panzer divisions.
I would also add, however, that I think that balance problems temporary motorization are in no way just a Soviet issue. It seems to me like a big balance issue for Germany as well, especially on turn 1 in the north/center due to the special movement rules that you can benefit from. Motorization of low quality units can also be, I think, preferable for Germany. Germany can motorize security divisions for 1 AP and about 500 trucks, whereas it costs 3 AP and about 1500 trucks to motorize a regular infantry division. If you want, after motorizing the security unit, you can also break it down into 3 regiments, but still only pay 1 AP (and about 500 trucks) for having previously motorized the entire division. What is more, since it uses less trucks to motorize those divisions, that means you will have more trucks left over to supply your motorized troops as well as your regular divisions.
Sure, the security troops will have low combat value, but does every mobile division really NEED to have a high combat value in the first few turns especially for Germany? I don't think so. Germany should be able to use its regular mobile divisions for fighting, and use motorized security troops for exploitation into empty hexes. There is going to be a significant amount of undefended territory somewhere, and with ~50 MP, Germany can just drive those units in and take a whole lot of free land quickly.
Germany can easily motorize e.g. 5 (or more, not sure how many exactly they start with?) security divisions on turn 1, for just 5 AP. That is pretty much a no brainer, IMO. Rush them forward with the Panzers for some nice very cheap extra ZOC blockers. Even if one or two of them were actually eliminated by the Soviets, that would hardly be the end of the world. As one example, Germany usually doesn't try to get to the Narva river on turn 2-3. However, you could always just send 1 security division there (or even just 1/3 of one security division), to force the Soviets to defend there before they really have sufficient troops to do so, to stop you from crossing it without a fight.
In principle it is a nice idea for a feature and it can make the game interesting and potentially more varied, so I would say it should not be simply removed as an option at all, but just (probably) needs some sort of rebalancing/adustment. I don't know what exactly would be the best way to do that, but there are clearly a variety of plausible options. But I would say that making motorization simply be delayed by 1 turn is probably not the best solution. The reason for that is that it favors the attacker. If e.g. you are Germany, you could then be resting your Panzers on turn 3 to build up CPP, and have the knowledge that you will do a bit attack next turn. So motorize a unit, and then it can be used to exploit and hold pockets along with the Panzers the next turn. Whereas if you are the Soviets, you don't know in advance which turns Germany will do a big attack, so you don't know when you will need to motorize.
Likewise with roles reversed later in the war when Soviets are attacking.
