And i believe you misunderstood me - no rocket sites will be mobile. That is for sure.
Let me clearify my suggestion:
Option A:
An engineer constructs a launch base. That base will then be able to construct missiles to fill it's silo. Once a missile is built, it can be launched at a specified target.
The launch base takes relatively long time to construct, and is decently expensive, but you only have to build it once. It will have a long launch range.
Option B:
An engineer builds a launch ramp, with a missile on it. The launch ramp cannot move, but is cheaper and takes less time to build than the proposed launch base.
Once the launch ramp fires it's missile, it "dies", or more specifically, it deconstructs, or sinks into the ground. This ramp has relatively short range.
Still, i agree with you on the strategical aspects; both options have pros and cons, i can list them here below:
Option A
Pros:
*Will have to be defended, in a safe position, yet near the enemy
*May provoke attacks from it's targets, thus make the game more exciting
Cons:
*When the enemy target is conquered, your missile base will be useless.
*You might end up having a lot of missile bases on the map, since you can't destroy your own buildings, yet constantly have to progress.
Option B
Pros:
*Since it has shorter range, you will have to get quite close to the enemy in order to launch. This makes the operation more risky, and requires more alertness from your enemies.
*You will have to defend your missile ramp while it is being constructed; if the enemy realizes that you are building missiles near their base, they will surely engage.
*This option keeps the map clean, since all ramps are either killed, or dissapeared through launch.
*This also makes missile launches require more micromanagement, since you have to pick a spot, defend it, and launch as planned, preferably without being detected (so that your enemy does not move his forces!), instead of just selecting a base and "build bombs/press fire".
Cons:
*The enemy target will be less specific; instead of setting your goal for a single base, you will have to keep a lookout for smaller launch sites. This makes large scale operations against missile bases less neccesary.