Yes, this is a great idea to reduce boredom and sitting out wars due to upgrades (esp. Heroes.)
Yes, but limit added builders to 1, completing the upgrade in 1/2 of the time.
Yes, but limit added builders to a total of 3, completing the upgrade in 1/3 of the time.
Yes, but allow this option for TOWN HALL 8 and higher only.
No, this is a dumb idea.