Based on a gradual convergence of experimental and theoretical results, the specific strength of raw CNTs will not exceed 50 MYuri [1 Mega-Yuri = 1 N/Tex = 1 GPa-cc/g]. A failure mechanism known as the Stone-Wales causes spontaneous defects in the Nanotube structure and limits the possible strength. Using 45-50 MYuri CNTs, we can expect a near-flawless spun tether to perform at 40 MYuri, and with a 33% safety margin, we can load the tether at a TSL of 30 MYuri.
Reaching a power mass density of 1.5 – 2.5 kWatt/kg is difficult. The best electric motors today achieve just under 1.5 kWatt/kg, leaving no margin for the PV panels. In order for the complete power system to reach 1.5 kWatt/kg, electric motor weight needs to be reduced by a factor of at least 2
Assuming extropolated technology space elevators are still feasible but space elevators are pushing what might be possible on several levels. More conservative space access systems would seem to be a better way forward.
We would use an existing nuclear bomb to send propellant at a large projectile which would hold what is being launched.
Full blown molecular manufacturing would provide higher power density for engines.
Space piers, rotovators and nuclear power launches would greatly lower launch costs and should be feasible far earlier than space elevators.
Remember that a 100 kilometer tall space pier is something that is about ten times more feasible than space elevators. More feasible in terms of the strength of materials that are needed.