I read that there are actually some elliptic curves that are cryptographically weak. For the PoW algorithm it's possible to deliberately choose a weak elliptic curve, since the keys only need to be difficult enough to calculate. That would prevent the finding of future algorithms that improve the calculation speed.

EDIT: On a second thought, a weak elliptic curve can in the future be found to be even weaker. So it's best to stick with a tested elliptic curve, such as the one used in Bitcoin for digital signatures: y² = x³ + 7.