Nixon's plan was actually better than anything we have on the table right now, and organized labor quashed it because they didn't feel it went far enough.
In fact, the Obama health-reform package Kennedy supported in his last days is similar to one Kennedy helped defeat when proposed by President Richard Nixon. If anything, the Obama plan is more conservative. Nixon would have mandated that all employers offer coverage to their employees, while creating a subsidized government insurance program for all Americans that employer coverage did not reach. It would take a miracle to pass such a plan today—a public insurance plan and an employer mandate are two provisions of the proposals now in Congress that are most in doubt.
Passing the bill as it now stands seems to me to be a case of not letting go of a bird in the hand.
From Mother Jones:
One of Kennedy's great regrets in life was not figuring out a way to cut a deal with Richard Nixon over his proposal to provide universal healthcare in 1971. He changed his mind in 1973 and came close to reaching agreement with Nixon, but by then AMA opposition combined with the distraction of Watergate took it off the table, not to return for another two decades. Steven Pearlstein provides a capsule summary here.
So you really hardly have to guess here. Kennedy had vivid personal memories of rejecting a healthcare deal because it wasn't good enough, and then watching the moment pass and having reform die utterly. If he were alive today, there's no question that he'd be fighting to pass the current bill, warts and all.