If more effective GPU miner will be released, simple changes in algorithm will make it completely unusable. For example, we can use bcrypt() result as salt. I.e. add stage in hashing process.

Current algorithm is:

1) Calculate B = SHA256(A)
2) Calculate C = scrypt(B)
3) Calculate D = SHA256(B, C)
4) Return D

Probably future algorithm:

1) Calculate B = SHA256(A)
2) Calculate C = scrypt(B)
4) Calculate D = bcrypt(C)
3) Calculate E = SHA256(B, D)
4) Return E

Like scrypt(), bcrypt() is also using many pseudo-random operations with memory during encryption process.