My main concern about this move is that it isn't clear how the nihilist can consistently regard her own preferred epistemic norms as more truth-conducive than any others (at least so far as non-deductive norms are concerned). I've previously noted that anti-skepticism requires us to regard some possible worlds as (a priori) objectively more likely than others, and that to explain rational induction (e.g. the projectability of "green" but not "grue") requires positing objective structure (something empiricist-inclined nihilists may also regard as unacceptably mysterious or metaphysically "queer"). If all possible epistemic norms are metaphysically on a par, as the epistemic nihilist seems committed to, then why regard any particular set of norms as more likely to lead to truth than any other?
Normative realists consider their preferred norms to also be metaphysically privileged in comparison to other possible epistemic norms and practices. The counter-inductivist and the grue-speaker are, we think, objectively irrational. They may consider themselves rational, but they are mistaken. The nihilist cannot think this. If "rational" in their own mouth picks out some stipulated set of norms that they just happen to endorse -- rational_green, say -- then "rational" in the mouths of the grue-speakers just picks out a different stipulated set of norms: rational_grue. Rational_green and rational_grue are on a metaphysical par, according to the nihilist; it's just that some communities use the term "rational" to pick out one rather than the other, but that's just an arbitrary semantic fact of no epistemic significance. The normative realist, by contrast, posits not just a semantic but also a metaphysical difference between the two sets of norms. Rational_green is privileged in a (language-independent) way that rational_grue is not. The realist may be wrong about this, of course, but my point is just that insofar as they believe this, it is not unintelligible that they continue to use rational_green norms and consider them more truth-conducive than rational_grue norms.
The key point then, is that the nihilist's continued attachment to the rational_green norms seems entirely arbitrary by their own lights. This renders their epistemic practices unintelligible, in contrast to the realist (who may or may not be correct, but at least is internally coherent).
* My thanks to grad students BK and SS, whose opposing papers on this topic prompted me to revisit my thoughts on the issue. Let me also mention that SS elaborates on the "arbitrariness" objection to the nihilist in a much more sophisticated way than I have in these rough thoughts!