Carbon nanotubes do possess a number of properties that would make them top candidates for very strong fibers.
At least in experiments on the micro-scale they have shown an extremely high modulus of elasticity and "inverse buckling properties" (that is they don't break easily).
To my knowledge (status of 3 years ago) there were still a number of problems such as
- how to produce large amounts of long nanotubes
- how to embed nanotubes in a polymer to achieve a tight connection between the polymer and the nanotube
- how to keep nanotubes distributed in the polymer (they tend to build lumps)
Nanotubes could possibly be the future, but it is still a long way to go.
CEitzi