“Being able to get a spacecraft to that platform without having to achieve full orbital velocity would save a lot of fuel.”
You’d save much more fuel just lifting a rocket to the upper atmosphere with a dirigible and then launching it from there, where you could avoid 90% of the atmospheric resistance, since that is where the really big fuel cost comes from. Even better, dirigible technology is old news, so we can almost certainly build something like that without developing much new technology, we just need to work out the engineering.