The main problem I see with it is that it implies wireheading as the optimal outcome.

AFAICT, it only does so if we assume that the environment can somehow be relied upon to maintain the wireheading environment optimally even though everyone is wireheading.

Failing that assumption, it seems preferable (even under pure hedonic utilitarianism) for some fraction of total experience to be non-wireheading, but instead devoted to maintaining and improving the wireheading environment. (Indeed, it might even be preferable for that fraction to approach 100%, depending on the specifics of the environment..)

I suspect that, if that assumption were somehow true, and we somehow knew it was true (I have trouble imagining either scenario, but OK), most humans would willingly wirehead.