In the same way that CICO (calories in, calories out) is a hard metabolic rule of weight gain, eating lot of complete protein and lifting heavy things is a hard physiological rule of "getting jacked" .
It's conceivable that future drug discoveries could safely reduce the amount of lifting required. But the protein requirements will always remain.
You obviously need some amount of protein as building material, but people eat much more than that because having a big excess encourages more muscle growth.
Not really, CICO is overly simplified to complete pointlessness. It's all hormonal, if you want to gain mass you can take a myostatin inhibitor which is a class of drugs that have already been discovered. You can also eat protein and lift heavy but that's just another way of managing your hormones.
These are very new and untested in large populations, but from everything I've heard so far it seems they still won't magically make you gain muscle without lifting heavy things and eating protein. They'll just take the limiter off when you do that so you can gain even more muscle than you would otherwise.
There is conservation of energy, you're not going to gain mass without eating, but if you change nothing else and take a myostatin inhibitor or any other medication that inhibits myostatin (like growth hormones) it is guaranteed you will gain muscle.
There are many people and animals who have dysfunctional myostatin so we already know what happens when myostation is inhibited.
Growth hormones inhibit myostatin so any regular GH or GHRP will help build muscle and retain it and the effect of these have been extensively studied.
It's conceivable that future drug discoveries could safely reduce the amount of lifting required. But the protein requirements will always remain.