Overall, tanks should be a bit faster. If OP's suggestion was implemented, the speed, sight, range, armour and cost became closer to their real performance, the performance disparities between the tanks would be more pronounced. Playing with tanks would be much more dynamic.
I agree with you on all this. If the reduced reverse speed were to be implemented, then all the tanks would also have to be radically redesigned, otherwise tanks made for head-on battles will quickly become obsolete. Don't get me wrong, I like the change, but a lot of changes will have to happen too not just to the tanks: like bigger maps, for example.
In the end, I can see a compromise for the vehicles: (Disclaimer, I only thought of these suggestions in about 5 minutes or so)
(All vehicles)
Slightly more range, handling/turn speed, slightly more acceleration
(Light vehicles)
Lower profile, better chance of being decrewed
(Medium tanks)
Cheaper, less popcap, slightly more speed
(Heavy tanks, tank destroyers, and heavy tank destroyers)
More range, more health, slightly more frontal armor, slightly better turn speed
Though with these reworks, I can imagine infantry and other units will need buffs too.
And 4v4s would feel like kursk.
Maybe it will actually get me to play more teamgames then. Love me some tank battles.