Actually if scrypt asic miners come out. Coins that we have mined now will be worth a lot more. And I think bigger and cheaper scrypt asic miners will launch at the end of 2014. i am not totally sure though. litecoin was launched in 2011, its enough time to make a cost effective machine within this time.
Well they are already out but the performance so far has been underwhelming. It's not like the SHA-256 ASICs that delivered 10x the hashing power overnight.
The other thing is that litecoin and other scrypt coins compete with one another. So even with ASICs the difficulty increase will be diluted across all these different coins. OTOH when it comes to SHA256 there is more or less only bitcoin. The rest of SHA-256 coins are just nowhere near the size of btc.
This is the reason I don't really care about Asics for Scrypt. There are so many coins that it won't effect the profit at large scale for GPU miners. Also Scrypt Asics are not as profitable as Sha256 asics so it is gonna take lots of time for them to go mainstream. I could be wrong though.