However, categorizing all those abilities makes improvisation uncomfortable. The player can say "I swing my axe at the goblin, trying to knock him off the cliff" but how does that interplay with Tide of Iron? Should there be a penalty there? Did you just give away a power for free? Did another player waste a power slot on that power?
You are right that Tide of Iron (and even more, I think, Bull Rush) provides a yardstick against which all "knock him in the pit" "improvisations" will be measured.
But, what happens without such basic powers in place? Pretty soon, a player has their character try to bash an enemy into a pit. After all, it's a pretty obvious thing to try. The DM makes a ruling on what happens. Now, here's the trick; the next time a player wants their character to bash an enemy into a pit,
hasn't that previous "precedent" set just as much of a yardstick as Bull Rush or Tide of Iron? As humans, we like system; we like consistency. If a system starts out with vague, hand wavey stuff about "improvisation" and "freedom for the DM to make rulings" then pretty soon the common "brilliant ideas" (i.e. most of the ones that are actually commonly useful) will be done in the game, and precedent will be set as to how such "innovations" are handled.
So, if you want to make terrain/zones and improvisation/stunts come up in play, don't list out a ton of options on the character sheet. Let people focus on the battle, looking for options in the battle, rather than focusing on their character sheet looking for options there.
The common (i.e. actually useful) "innovations" will soon generate precedents - and then you are back where you were with 4e. Except actually worse, since, unless these basic manoeuvres are defined in the system, rules like "give Fighters advantage whenever they try these manoeuvres" are impossible since there is nothing to specify the advantage for.
I've said it before, but "innovating" by making up stuff not covered by the rules is not the only way to improvise or show creativity - it's just the easy, cop out way. The way I much prefer is to see improvisation and creativity
inside the rules. With my current 4e players I see this a fair amount; they are focussed on the map, not on their power cards, and they are sometimes using At Will powers (when they have Encounter powers left) because they see an opportunity to make
someone else's Encounter power more effective by doing so. Creativity to feed into each others' attacks as a party is great, IMO - I love to see it in 4e and I would love it if I saw it really encouraged in Next.
Oh, and someone mentioned that "some players seem worried to lose their "rights" to the DM, but it shouldn't be Players vs. DM". My answer would be that I don't think it's the DM such players are worried about; it's other players. Without good rules for all common manoeuvres, my experience is that it pretty soon comes down to who, among the players, can sweet-talk/double-talk/bluff the DM best into letting them get away with more and better "improvised" things. So often I have seen one player suffering relative superiority at the table because they can blag stuff past the GM, either because they are just a good persuader, or because their tastes and beliefs align closely with the GM's, or because they read the likes and dislikes of the GM well. I generally like some friendly competition between players (akin, perhaps, to the archetypal "orc counting" between Gimli and Legolas), but "skill based" play aimed at manipulating the GM to the maximum extent possible just makes my lips curl.
