One thing I was thinking about some time ago was that if you wanted such infrastructure while still being able to adjust azimuth and elevation, perhaps an artif

One thing I was thinking about some time ago was that if you wanted such infrastructure while still being able to adjust azimuth and elevation, perhaps an artificial lake would work? At the very least you avoid salt water this way. Of course at that point you can't pick and choose your launch site after the fact, but that's not a regression compared to stationary launch pads anyway.