I've used spectra (dyneema) in caving. It's the perfect material for SRT footloops. Here's what Marbach & Tourte say in Alpine Caving Techniques:
The optimum material for this application is Spectra cord (or Dyneema), a rope made of specially extended chain polyethylene fibers, which is well suited to caving. It is so light that it floats on water; it is inelastic yet is stronger than steel, which allows us to use diameters as small as 5mm. It is six times more abrasion resistant than nylon, and it is easy to melt the ends to prevent fraying. Always choose 100% Spectra cord (including the sheath) if possible, as it is the most abrasion resistant variety. It is completely white because Spectra cannot hold a dye; any cord having colored fibers indicates that it is a nylon blend.
And on light rigging:
Even in light rigging, it would be pure insanity to use 5-mm Spectra cord as your pit rope. ... Spectra is as static as a steel cable; in the event of an anchor failure, the resulting shock load could be critical.
They also give this wonderful quote, when discussing the limits on light rigging:
Trying to combine the advantages of nylon and Spectra would be like trying to crossbreed a fish and a rabbit, and we would then need to invent the appropriate mechanical devices.
Spectra would be unsuitable for racket strings. It would be impossible to string a racket, because spectra does not stretch (well, no more than steel does). Even if you could somehow tension spectra, it would be useless for playing, for the same reason. I suppose you could try blending it with other materials to increase durability.
As a racket material, I have no idea. It's light, strong, and inelastic. I'd be amazed if you could make a racket out of just spectra, but perhaps you could blend it into a carbon fibre mix. I've no clue what the result would be, though. Maybe you could use it to create a thin, super-strong shell around the frame, to increase durability.
When assessing this material, bear in mind it's low melting point (about 150 Celsius). Spectra and Dyneema are actually brand names; the material itself is ultra-high-molecular-weight polyethylene.