Yes I agree, though it's too early to go for such ideas...I'm sure once they start making new features we will see all sorts of cool things

Well, there's two potential problems with this:

First off, if one player can do something that affects the whole game, that means it can affect his teammates too, and the developers seem to have gone through quite some lengths that you can't do anything harmful to teammates... the only exceptions I can think of are Erebus's hp potions (which isn't under your control), and Rook being able to drain hp from friendly buildings, which is rarely an issue anyway. Being able to affect teammates either purposefully or accidentially really kills the trust you need in a team strategy game like this. Even something seemingly benificial can make people on your team angry... for example, buying priests straight off.

Second, if you wanted to put mini-missions in a map... where would they go? The maps are pretty small and spartian, and teleporting off to a mini-level to complete an outside objective would allow the other team to make some major progress in the real match.

While I will admit the game needs more variety, I think these are all bad ideas.  If your character gets more powerful in the course of the round(which I think we can all agree is a fun and good mechanic), it should only be as a reward for good performance earlier on in that same round.  It should not be because you weren't screwed in the first thirty seconds by the map pouring a vat a of boiling lava over your head or you were closer to the special enemy when the game randomly decided to spawn it or you've played more total games.  The reason for this is very simple, the game must be fair to be reliably fun.  It doesn't need to play out the same way every time(in fact it shouldn't, variety is what makes a game interesting), but it does need to be fair.  It is frustrating to obviously outplay someone, but for them to still have the edge because the game rewards something other than skill(if you disagree with this, then please never ever make a post with balance suggestions because to deny this is to deny the reason for balancing the game).  It is boring to win by a huge margin(if you didn't believe this, you'd just be bashing the easy AI ad infinitum), and with random occurrences on a scale large enough to matter to the gameplay, you don't even know if you can prevent this from happening by playing with a guy you know is just as good as you.  The fact is, fairness will give you a reliably good experience.  Randomness and extra-round advantages will not.