Are there proposed hardfork changes that couldn't be made if the market was filled with ASIC miners? Suppose a year from now most of the hashrate is being produced by ASICs.

Bitcoin is not feature-complete yet. Out of the changes in the hardfork wishlist, would any of these changes be hard/impossible to implement on ASICs that have been sold already?

To make such breaking changes, it most likely that a majority of the mining power will be needed. If ASICs become the majority, and they can't adjust to these changes, do we have a problem?


I say "most likely we need a majority" because maybe breaking changes could be done without a majority of hash power, but rather a near-majority, accompanied by strong user support. But it would certainly make life more complicated.
As long as no changes are done to the structure of the block header, the ASICs should work just fine. There are some proposed changes that could alter it, like protecting the block chain against pre-mining, or adding a new field to the block header.

So yes, when the ASIC miners become the majority it will be hard to push those changes unless Bitcoin faces some serious issue that forces the change (for example, an attempt at a 51% attack).