I think there's still chance to make some changes, but not in the same scale as say the OKW rework. I think you need to maintain the same "framework" while adjusting small bits which can give you different timings and accessibility of the units.
1-Swapping units from tiers.
This one i think is the most tame one and the one most likely to be used. That been said, the only combination i could see be done is:
Cpt: 50cal, Pack Howi, Stuart
LT: M20, AT gun, AA HT
From here on out, i think the free officer system needs to be adjusted. Which makes things more complicated.
2-Making tech cheaper, while removing free officers. This would be mostly a mp based thing.
3-Same as point 2, but locking down certain shock units behind a further tech upgrade.
For example: in the current roster, locking down AA HT/Stuart and later on Sherman/Jackson. In the case of the major, this is for improving the timing of certain call in vehicles.
I don't see this working to be honest, I thought a lot about how swapping units and it simply doesn't work.
Combo HMG.50 + Stuart is always going to be a better choice than AAHT + M1Atg. AATH and ATG a pure support units you can't really expose unlike the stuart and HMG.50.
Atgun can't support well the AAHT because the first threat for your AAHT isn't infantry, isn't Lv's but Atguns. Pak40 or raketen only need two hits to wreak it.
On the opposite, the only significant danger for the Stuart is the PUMA, which can be handled with good micro, then the HMG.50 can deal with infantry and retreat if needed.
Above that, HMG.50 + pak howitzer + Stuart, that's a great combo! The AAHT would need a serious buff to make it appealing vs it, and a kind of buff no one is going to accept.
Second point, removing officer and adding tech layers to unlock faster certain units is a possibility to explore I agree with that.