I'm not certain from reading 716 as to whether or not the player who originally suggested the shortcut is able to genuinely further shorten it, or if what's meant by "each other player" means that once a shortcut has been suggested, only the other player(s) are able to truncate it before the game-state is agreed upon and advanced.

716.2a At any point in the game, the player with priority may suggest a shortcut by describing a sequence of game choices, for all players, that may be legally taken based on the current game state and the predictable results of the sequence of choices. This sequence may be a non-repetitive series of choices, a loop that repeats a specified number of times, multiple loops, or nested loops, and may even cross multiple turns. It can’t include conditional actions, where the outcome of a game event determines the next action a player takes. The ending point of this sequence must be a place where a player has priority, though it need not be the player proposing the shortcut.
Example: A player controls a creature enchanted by Presence of Gond, which grants the creature the ability "{T}: Put a 1/1 green Elf Warrior creature token onto the battlefield," and another player controls Intruder Alarm, which reads, in part, "Whenever a creature enters the battlefield, untap all creatures." When the player has priority, he may suggest "I’ll create a million tokens," indicating the sequence of activating the creature’s ability, all players passing priority, letting the creature’s ability resolve and put a token onto the battlefield (which causes Intruder Alarm’s ability to trigger), Intruder Alarm’s controller putting that triggered ability on the stack, all players passing priority, Intruder Alarm’s triggered ability resolving, all players passing priority until the player proposing the shortcut has priority, and repeating that sequence 999,999 more times, ending just after the last token-creating ability resolves.

716.2b Each other player, in turn order starting after the player who suggested the shortcut, may either accept the proposed sequence, or shorten it by naming a place where he or she will make a game choice that’s different than what’s been proposed. (The player doesn’t need to specify at this time what the new choice will be.) This place becomes the new ending point of the proposed sequence.
Example: The active player draws a card during her draw step, then says, "Go." The nonactive player is holding Into the Fray (an instant that says "Target creature attacks this turn if able") and says, "I’d like to cast a spell during your beginning of combat step." The current proposed shortcut is that all players pass priority at all opportunities during the turn until the nonactive player has priority during the beginning of combat step.

716.2c Once the last player has either accepted or shortened the shortcut proposal, the shortcut is taken. The game advances to the last proposed ending point, with all game choices contained in the shortcut proposal having been taken. If the shortcut was shortened from the original proposal, the player who now has priority must make a different game choice than what was originally proposed for that player.
With this hanging overhead, imagine the following sequence:

Player A: (after demonstrating an infinite combo)"...so, I'll generate 10 billion Blue mana?" <-shortcut proposed
Player B: "When you're tapped out for the first time, I play [answer card]." <-shortened!
Player A: "Well, you won't be able to, because instead of passing priority for the first effect in the sequence I'm going to use Aether Vial to put Meddling Mage into play, naming the spell you just told me you'd cast to 'wreck me'."

So, bear in mind that I've never seen this happen and that for as long as I can remember everyone typically treats this situation as though Player A were too late to use Meddling Mage in this way -- they essentially act as though the loop has de facto already started and so everything being suggested is actually occurring in response to Player A going off, when really the Comp Rules appear to handle this by saying all players agree on the future state of the game, then move to that game state as a reflection of the suggested choices. So the suggested response to the combo is not on the stack, in fact nothing may be on the stack while the shortcut is being proposed.

If this is at all legitimate it would be one of the biggest dick moves of all time, or at least it would make Meddling Mage playable in an alternate universe. I'm inclined to think that this rule doesn't actually give Meddling Mage superpowers -- I'm just having trouble rationalizing how it doesn't, without robbing Player A of the chance to re-shorten his opponent's suggested shortcut (which is a shortened version of Player A's original shortcut).