Sorry, don't want to hijack your suggestion, but I have a similar suggestion, which is not exactly same but, since it could offer something towards your own goals, I am posting it here.
Imagine this amazing announcement.
We have added a new body part - SHIELD - equip your creeps with this new and extra shiny body part to protect your screeps from harm. SHIELD will absorb all hits on the body part, but will use up 1 energy for the X damage absorbed. Your screep will also need a CARRY body part to keep its shield charged,
But wait, this is not all - the new amazing body part from the Spawn Werks(TM) also includes an ability to prolong life of your creep by utilizing advanced gene-editing techniques. It won't keep your creep alive forever, but will prolong its life per rate of Y energy per tick.
Imagine the siege battles, with tankers and fast supply tenders, defense of the supply lines and daring raids into the enemy territory to choke off the flow of energy.