Completely off-topic, but what's the latest thinking on space-elevators? Is there any active research on them? I thought that carbon nanotubes or diamond nanothreads were likely candidates for the cable material.
Probably the biggest barrier to space elevators is exactly what SpaceX and Blue Origin are doing - safe, reliable, and eventually (relatively) inexpensive rockets will make the large fixed costs of setting up a space elevator uneconomical.
However orbital vertical tethers are doable with Zylon. A series of 3 orbital tethers could move stuff between LEO and the lunar neighborhood. http://hopsblog-hop.blogspot.com/2016/08/tran-cislunar-railr...
Both Musk and Bezos seem well on their way to reusable boosters. But reusable upper stages is another story.
An upper stage re-enters at around 8 km/s. An ~7 km/s delta V budget plus the need to carry a payload means a very slim dry mass fraction, an egg shell space craft.
Recovering and reusing upper stages will be much harder than reusing boosters.