Bernie's free college idea has convinced Matt Yglesias on the merits, but as he argues later, it's not that practical. Universities are run by states, and so Bernie's plan relies on matching funds at a 2-1 level. Total tuition at all public colleges and universities is only $70 billion, so the feds would pick up 2/3rds if states would pick up the other third.
Probably a lot of blue states would jump at this idea (the University of California alone contains 238,000 students), but as Yglesias notes red states assuredly would not. There's only so much leverage the feds have over states, and it's pretty tough to convince states that are dead convinced on pummeling their own citizenry.
And that's fair enough, policy design does matter. However, as with the single-payer scuffle and the ensuing extremely irritating debate about whether Bernie was being sufficiently deferential to the WONKS, I think much of unpolished policy can be chalked up to him being a political outsider for basically his entire national career before this year.
When you're a left-wing critic railing against centrist compromises like Obamacare, it's really not necessary or practical to have completely worked-out policy proposals for every single idea. For single-payer, for example, you just look at places like Canada or Taiwan, conclude that the basic idea is workable, add the obvious fact that Obamacare isn't going to cover everyone, and then put forward rough outlines or utopian bills.
But now that Bernie is a national contender making Hillary Clinton fight hard for the nomination, suddenly he's got to have "serious" proposals to impress the high-status DC gatekeepers. Unsurprisingly, they're often bit rushed, and sometimes don't have all the t's crossed and i's dotted policy-wise.
I see no reason to be unduly concerned about this. So long as his ideas are not completely impossible (and he has gone too far in some areas, to be fair), then it's the basic workability that matters. If he were to win, the details can be filled in later, when he will have command of the Democratic Party intellectual apparatus. I think a lot of "wonk" criticism of Bernie is more about affect and cultural deference than it is about policy (recall how Ezra Klein, a prominent Bernie critic, was briefly snookered by Paul Ryan).
And speaking of free college, what about Freddie's idea for five big new federal universities? Simple, utilitarian, cheap, administrator-lean, and free for any American citizen. Put the enrollment target at 100,000 per school and go from there.