I think the discussion about Warlords is going to be something that comes up a lot.
One of the biggest innovations in 4e was the out of turn action. Granted, you do have out of turn actions in other editions (Attacks of Opportunity from 3e, for example) but, they were very limited and often it wasn't something you could initiate.
4e breaks that mold. In 4e, it's not unusual for a given player to act on his turn, on an opponent's turn and on an ally's turn, all in the same round. And, the player could have initiated all three of those actions, if they are reactions of some sort.
Which brings us back to the warlord. One of the people at my table commented that when you play a warlord, you don't play just a character, you play the entire party. And to some extent, that's true. A warlord shines by using the other characters in the party.
If Next does not allow for out of turn actions, then the warlord concept, as envisioned in 4e, isn't possible. Yup, I could push a target next to an ally. However, that ally doesn't get to attack - or take any other out of turn action. He has to wait until his turn to take an action. If the opponent goes before my ally, it's entirely possible for that action to be wasted - he simply evades the ally, stepping away, and I'm out an action.
Now, if by "improvise an action" you mean that I, as the player, can say, "I'm going to push that orc into Bob's character and shout at Bob to attack him" and Bob gets a free attack, then, no fuss no foul. But, I highly, highly doubt any DM would do this without very explicit rules for it in the books. As an improvised action without any mechanical backup? IMO, highly unlikely.
