I didn't want to dig into it too much, cause I don't understand the electrical aspects very well, and I am really pushing my knowledge even with the general concept of a rotating space elevator. Looking through the document published by JPL in 1989 it certainly looks like a well-researched concept with the fundamentals written well over a decade ago (and well beyond my understanding at that). In fact, unknown to myself and many others, my own country (Canadian Space Agency) launched the longest-ever electrodynamic tether into space on a sounding rocket in 1995...

Oedipus-C Sounding Rocket

There was a previous attempt by NASA in 1992 to test a much longer 20-kilometer conductive tether, but a malfunction caused the unreeling mechanism to stop at 256 meters. There have also been longer non-conductive tethers launched successfully to test passive momentum transfer between satellites and tether survivability in space.

This process has been very slow to develop in comparison to other space developments. Especially considering that USA went from nothing to repeatedly landing a man on the moon in under 10 years. Space tethers is a comparatively poorly supported area IMO.

First use of a space tether 1966 AD

Last 10-years of Space Tether experiments

And of course the upcoming ProSEDS experiment:

ProSEDS 2002

This new experiment will test the satellite-deorbiting capability of an electrodynamic tether. So far no scheduled tests for a tether-based stationkeeping engine. Either this field is unpopular or it is hard. But it appears destined to replace rockets in some very specific areas, particularly stationkeeping applications. For example a tether-based stationkeeping system will save $2 billion in costs on the International Space Station over the next 10 years by eliminating dedicated stationkeeping propellant resupply launches.

I would see this as the most significant leap forward for the space program since the Apollo Program. That is unless I discover something better.... I always do.