I thought backtracking is exactly how RecDescent does selection between multiple alternatives.

But anyway, I don't see this as an obstacle here. The desired behaviour could already be achieved if there was some way to write an action that would only be executed in case the rule it is placed in is committed.

And I don't see any way to do so. I thought of using the $commit variable but it shows the state of commitment to the current production, not the whole rule.