I won't go with "nothing". My answer is, "whatever is profitable enough to invest in ASIC design and development". So, if X11, or BobsMagicHashingFormula becomes the next big thing, then somebody will develop an ASIC for it. If there's money to be made, somebody's going to make it 
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.Perfect answer. You will notice coins say asic resistant. They do not uses (or should not) proof. If there is a big enough market share there will be a product for it.
A n/x11 would be nice but I don't know if or timeline we will see that. Scrypt and of course SHA-256 are controlling the game right now.