I’m not sure why I’m wading into this, but probably because I read this and this and this and this and at least some of the things linked to within those pieces. Why that means I have to add my 2c I have no idea, but that must be why I’m a blogger. (Moshe Idel to Harold Bloom: Harold, just because you read a book about the kabbalah, doesn’t mean you have to write a book about the kabbalah.)
“Liberaltarian,” besides being singularly aneuphonic, suffers, I think, from an asymmetry in its parts.
“Liberal,” like “Conservative” defines a broad intellectual tradition, a general political temperament, and a particular side in a variety of contemporary political disputes. “Libertarian,” like “Socialist,” defines a particular and distinct ideology (albeit one broad enough to have a significant number of subsidiaries – paleo-libertarians and cyber-libertarians, Marxist and Fourierist Socialists, etc).
A “liberaltarian” then should be something like a “social democrat” or a “Christian democrat” – that is to say, first and foremost a liberal democrat (small d), but with a partial affinity for a specific total ideology (libertarianism, rather than Socialism or Catholicism). An ultramontanist would probably not have much use for Christian democracy, and a Trotskyite probably wouldn’t have much use for social democracy. Similarly, I wouldn’t expect a paleo-libertarian or an anarcho-capitalist to have very much interest in a “liberaltarian.” Point being: if there is such a thing as a liberaltarian (and I do think there’s some use to the term, though I’d prefer another nomenclature), that person is first and foremost a liberal.
The analogy to “fusionist” conservatism, meanwhile, is fatally flawed by the fact that fusionism was an oppositional alliance rather than a tendency in and of itself. One could imagine a world in which “theoconservatism” dominated American politics, and even the opposition tended to frame its arguments in “theoconservative” terms; in this hypothetical world, one can imagine a “progressive/libertarian fusionism” comparable to the movement conservative fusionism that grew up in 1950s America. But that’s not the world we live in.
In our world, in practical terms, a liberaltarian is someone who is fine with the welfare state but opposes the nanny state.
Finally, it seemed to me from the very beginning that the most promising area for potential cross-fertilization between liberals and libertarians was in foreign policy and attitudes towards the military. After all, we do live in a world in which one party (the GOP) is dominated by what critics would characterize as militarist thinking, and in which the other party has a strong tendency to respond in similar terms. If you want to look for a real basis for a left-libertarianism “fusionism,” that’s where you might find it.