This website is still up, and was last updated in January.
http://boston-halifax-ferry.com/
So it looks like the idea is not dead, though I'm wondering how well-accepted it would be by the government/taxpayers given the Nova Star situation. That's assuming they will need subsidies to get it up and running.
While it is better in some ways, as it travels between major cities for their respective areas, it does also compete with the Nova Star in that they both cut off the drive around New Brunswick and most of Maine. To compare them straight up in going from Halifax to Boston, the Nova Star would take another 5 hours of driving from destination to destination. Given the political bonus of bolstering the south shore's economy a little, I question whether the government would allow such competition for a presently subsidized service that has political implications.
Would be interesting, though, the idea of driving on a ferry in Halifax and waking up in Boston is an attractive one, I'll admit.