Hmmm that sounds pretty good, but in Isengard 'Some evil gives speed to these creatures, sets its will against us'
(didn't find the book quote hehe)
The mechanism you say reminds me of the passive ability given to the exiles at its camp.
The thing here is allies didnt arrive that fast, Gondor was pretty much alone, begging others to come. I get it will only be speed bonus, but when the suicidal mission of Faramir failed, its return was scary and painful. It was only until Gandalf appeared, the knights got a relieve.
Maybe it could work the way you say, but only the way of the settlement counter part you choose, thus this battalions could move faster.
The animation could be: lit the beacon, then an errand rider using the new mechanic of the dwarven resource wagon used at Dale, marking its road, arriving to the settlement, thus summoning the emergency battalions, that will move faster if and only if use the road previously marked.