What "new" experience will any new addition of tanks really provide? - They can shoot a cannon at other tanks or infantry and the coaxial MG and perhaps even a bow MG at infantry and lightly armoured vehicles. They will also be able to destroyed themselves by other tanks or infantry Anti Tank weapons like the Panzerfaust etc etc. Bringing new vehicles will not add any new experience but it will add to the flavour of the game and that alone is reason enough for adding the T-34 Model 43, Pz III M, StuG IIIG etc. etc. Having a 100 mm gun on a SU-100 will not change the game in a dramatically new way as we already have the 122mm maingun for the IS2 nor will introducing the Tiger II.
In short any new addition of vehicles to RO will not change in how the game is played or the balance of power but it will make the game more diverse for the mapmakers.
I'll try to explain this here. When I say it'd be a different game experience, I don't simply mean the "Tanks shoot at other tanks". Although that in and of itself is something pretty different about early-war tank doctrine -- the ROLES of the tanks were much more varied than the mid and late war tanks. Bear in mind that role aren't always identical. You can have a heavy infantry tank or a light infantry tank, for example.
Early in the war, armored forces were pretty heterogenous. I'll use some examples from the German tank forces. Take the Pz IV D (which is similar in many ways to the F1 in game). The Pz IV D has a short barreled 75mm cannon. It's designed primarily as an anti-infantry platform, as evidenced by the fact that it shoots shells at a lower velocity than its counterpart, the Pz III. The Pz III is primarily designed for anti-armor work. It shoots a smaller, but higher velocity round. Early in the war this was a 37mm round, but it gets upgraded to a 50mm round by the time of Operation Barbarossa. As I understand it, both tanks had a similar top speed, and were designed to operate alongside each other. Both were of "medium" weight, and the Pz IV, as you know, was later redesigned to operate in a more "universal" role where it could take on both enemy infantry and enemy armor.
That division of labor alone -- the difference between an anti-infantry tank and an anti-armor tank (not necessarily a tank destroyer, though) is drastically different from the mid-war "Medium tank" that simply does it all (or at least does a lot of the work equally).
By contrast, consider the following two types of tanks, which were more prevalent in the early war:
Infantry tanks: generally slower-moving, heavily armored tanks designed to move alongside the infantry, and to provide anti-infantry and anti-fortification support. They were designed to punch holes in enemy lines.
Cruiser/cavalry tanks: Lighter armored and with somewhat lighter weaponry, these tanks were supposed to move quickly (as the name implies), and to take advantage of the existing holes in enemy lines that had been created by the infantry tanks and infantry.
Now, bear in mind that, as I said, you can have both light infantry tanks (IE: T-26) and heavy infantry tanks (IE: KV-1, KV-1S, KV-2).
All of these tanks have very different strengths and weaknesses that a competent tanker must play to. For example, the BT-7 tank has a very high top speed, but relatively light armor and a 45mm main cannon. That's drastically different from a T-60 which has somewhat heavier armor, but a slower top speed, and which mounts a 20mm cannon.
If you try to drive EITHER of those tanks the same way you do, say, a Pz IV H, you'll end up getting yourself killed quite a bit. On the other hand, if you use the tanks in their intended roles, or play smart and use them to take on the right targets (IE: take a BT-7 up against Pz IIIs and Pz IVs using flanking maneuvers and capitalizing on its speed; take a T-60 and put it in an anti-infantry or anti light vehicle role) you may do pretty well. Some of this will also depend on the forces you face.
But like I said, you can't drive these vehicles like the standard medium tanks we have and expect to do well. THAT's where the difference comes in -- in the way the player has to adjust their tactics to suit the equipment, rather then "Oooh, look. It's a T-34 with a different shaped turret." Or even "Hey, look, it's ANOTHER big heavy German tank that parks somewhere and shoots at stuff".