Tim York wrote:My main criterion for second choice is that, like Pinot, the grape should be capable of achieving consistently great results unblended.
That rules out Cabernet Sauvignon, Merlot, Grenache, Syrah (except in Hermitage), Grenache, Mourvèdre, Tempranillo and the Portuguese varieties. Much as I love Chinon, Bourgueil and Saumur-Champigny, it rarely is really great, so I disqualify Cabernet franc.
That leaves Nebbiolo easily in second place with Sangiovese following some way behind.
Greatness is in the eye of the beholder of course, Tim, but I find great unblended Syrahs from Cornas as well as Hermitage (in fact, I find more of them in Cornas than in Hermitage these days). In fact, the only great Syrahs IMO that are blended are Cote-Roties and even then it's debatable how much Viognier character is really evident in the "blend." And, to me, some of the greatest expressions of Mourvedre are the Bandols of Domaine Tempier, and they are unblended, too, are they not? Having said all that, though, I can't quibble with your choice of Nebbiolo, either.
Mark Lipton