I do think that the GOP tactic of attempting to keep agencies from functioning by filibustering any possible nominee is a big deal. I'm not sure whether it's an entirely new strategy -- wasn't there a similar situation with the FEC a few years back? -- but I do think it's a highly significant case of Constitutional hardball.
But is "nullification" the right word for it? Neither Tom Mann nor James Fallows is particularly quick to use overheated rhetoric, and they're the two that have pushed the term, and I'm reluctant to disagree with either of them. Seth Masket, however, argues that there's a key difference: Constitutional hardball (as Matt Glassman points out) is by definition staying within the literal rules of the game, while 19th century nullification was most certainly not doing so. So I'm sort of with Joshua Huder in not particularly feeling very good about calling the current GOP tactic by the same name.
I suspect this ship has sailed, but I wish I had an alternative name to substitute for "nullification" that would similarly denote the seriousness of this particular form of Constitutional hardball without implying that it actually crosses over into breaking the literal rules of the Constitutional system.