Some historical answers:
-The T-34 with the U-11 gun was an historical project, but it had a different turret.
-There were no SPG projects for the E-50 and E-75 chassis types.
On interesting Czechoslovak stuff, like in-game implemented projects: We will give information when we will develop the tree.
-When T-50-2 was in game, it had unhistorical characteristics. Therefore we implemented the MT-25.
-We do not need a tier X Chinese replacement.
-We do not have candidates for a second Chinese Heavy/Medium branch.
-The unhistorical T-54 engines are a question for the balance department.
About the original Tiger P:
-Rhm. Borsig had its chassis built in real life, but nothing more than that.
-I do not know any historical details about the Chinese T-34-3. But the Soviet one had 3 guns:
See you, everyone!