The HoMM brand is not about breathtaking graphics - we don't need you to win prizes like Half Life 2 on their innovative Havoc engine. Heroes should have an addictive gameplay, and I don't think there's any need to add a zooming option! I know many fans will hate the idea, although it is bold!
I can promise I'll buy the game on any case, just like I bought the first Heroes when it first came out.
Zooming like in games such as Ground Control, Act of War is somewhat wrong and will spoil the magic of this game. But if you must, perhaps you could limit the zooming option - like have it zoom in three zoom levels.
Keep the addictive gaming alive, please!