Would it be unbalanced to allow Extra Attack on a ready action?

Question

The rules for D&D 5e clearly state that Extra Attack can only be used on the character's turn:

Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

This on-your-turn restriction occasionally leads to scenarios in which creatures that roll a low initiative seem to have substantially better tactical positions in the turn order. The simplest example is when two level 5 fighters begin combat 60 feet apart. The fighter with the higher roll is faced with a choice: (1) dash up to the other fighter or (2) ready an attack action and (optionally) move closer. In case 1, the slower (lower initiative) fighter gets a full attack round before the faster fighter gets any attack. In case 2, the slower fighter has the option of moving to a stalemate position (i.e., where the faster fighter would be in an equivalent position on their next turn) or, if the faster fighter moved close enough, moving into range and attacking the faster fighter. At best, the faster fighter is going to attack the slower fighter once while the slower fighter will be able to use all of their extra attacks, not to mention a bonus action and reaction.

This example is contrived, but I've experienced versions of it in actual play. Simultaneously, I haven't been able to think up any situations in which allowing ready multiattack would be tactically unfair—this doesn't feel right to me, though. What am I missing?

On forums I've seen it conjectured that readied actions are disempowered to keep combat and initiative manageable, and this makes perfect sense to me, but I'm wondering if allowing readied multiattack would unbalance the game mechanics for a group and DM that enjoy tactical complexity.

Answer 1

The damage output does not increase

If you take Extra Attacks on a Reaction rather than your own turn you don't get to make more Attacks than you would otherwise. In essence you trade your Reaction for a potential advantage in positioning or timing.

Extensive use of Ready can affect gameflow

If Ready is extensively used, there are two potential problems for the flow of the game that I noticed.

1. The initiative order makes combat easier to track but Ready will normally upset the sequential handling of actors making combat somewhat harder to track. If multiple Actions have to be resolved during another actor's turn, this is of course exacerbated. You have to decide for yourself if the extra tactical options outweigh the extra mental load.

2. Ready can promote stalemates, especially with ranged attacks, if all participants wait for the other side to move so they can get the most favorable attack. While allowing readied Extra Attack gives an increased benefit if such a strategy works out, the likelihood of this being useful mostly depends on how encounters are designed. And this is a problem that a normal readied attack can also create.

Besides the flow of the game, an argument of realism can be put fourth because reactions are described as quick actions, such as making a single attack (opportunity attack) or pulling a lever. Whether or not realism in game mechanics has any importance is for you to decide. But if you want to have the best tactical combat, it's probably not so important.

In the end readied Extra Attacks make Ready somewhat more useful and somewhat harder to handle, so you have to decide:

1. Do you like Ready being heavily used or at least do not mind? Considering how much it is already used in your game.
2. Do you want to handle the extra mental load of off-turn Extra Attacks? Is it worth extra tactical options?

If the answer is yes to both you can allow it.

Answer 2

Limitations increase tactical complexity. Extra options which have approximately the same results only increase decision paralysis.

While it would not unbalance the game, because a smartly phrased ready action is about as likely to proc as simply taking an action on their turn as normal, it would create a situation where there are extra options of approximately equal effectiveness, which defeats the point of complex strategic decisions.

Contrary to your stated goals, leaving this mechanic RAW is what creates tactical complexity, because the player must decide for themselves whether the Ready Action they want to take is worth sacrificing an Extra Attack that would otherwise be owed them. A Ready Action is a tactical decision, and as such comes with drawbacks. It may not proc at all, and it may not have the intended results. Not being able to use extra attacks is a built-in drawback of this action, and players must weigh it against the benefits of taking an action on their turn.