Eventually the difficulty curve we have seen on scrypt and 256 will level off. Scrypt is a different beast with asics because there are so many coins to absorb the hashrate. Scrypts earnings dropped faster than bitcoins ever has, but its leveling off faster as well.
I beg to differ. Number of coins doesn't matter much because LTC is ~80% of all Scrypt hashrate. And at the current rate of ~900 GH/s a couple of thousand of these Titans or Vaultbreakers or whatever can easily DOUBLE the difficulty, if these miners are actually delivered and up to spec. Even Bitmain with it's L1 can slaughter Scrypt profitability. I don't know why it has leveled off recently, maybe because Zeus hardware killed the profits for itself and of course for GPUs, maybe because GAW stopped selling hardware, but I wouldn't expect this to last. More efficient ASICs will come eventually.