Twisted curves in protocol I've come to understand that twisted curves, as for instance defined in the Brainpool specifications, are $F(p)$-isomorphic to their regular $F(p)$ equivalents. So brainpoolP256r1 is isomorphic to brainpoolP256t1.

In a protocol, does it make sense to specify support for twisted curves? Should it be possible to specify the twisted curve OID instead of the $F(p)$ equivalent? If so, could using the twisted curve representation of the curve have any performance benefits over the regular representation? Or is the twisted curve representation only used for the security analysis of the curve?
If so, could using the twisted curve representation of the curve have any performance benefits over the regular representation?


Yes, at least in some cases. To quote Twisted Edwards Curves (section 7):


  One can choose $a$ to be very small, making twisted Edwards curves essentially
  as fast as Edwards curves and thus bringing the speed of the Edwards addition
  law to a wider variety of elliptic curves.
  
  Even when an elliptic curve can be expressed in Edwards form, expressing
  the same curve in twisted Edwards form often saves time in arithmetic.





  Or is the twisted curve representation only used for the security analysis of the curve?


In addition to the above, twists can also be used to make ciphertexts indistinguishable from random data like in A Public-Key Encryption Scheme with Pseudo-Random Ciphertexts (pdf).