But is it meaningful to talk of spending a year or more of subjective time accelerating at 1G? According to the Wikipedia page you link to, it does not become

But is it meaningful to talk of spending a year or more of subjective time accelerating at 1G? According to the Wikipedia page you link to, it does not become harder to accelerate a spaceship the closer it gets to c, at least from the point of view of its occupants. So you've been accelerating for ~300 days (shipboard time), and you're now nearly at c. In fact, you're only 10m/s below it, so you should reach light speed in a bit more than a second. But we know that's never going to happen, because it can't. I'm assuming (I don't know, I'm a layman) that that final second-and-a-bit will stretch like taffy, in time-dilation terms. You're already travelling at 0.999999966c, at which for every second of shipboard time more than an hour will pass on Earth. Dilation will only increase the closer you edge to c: at some point, every yoctosecond of shipboard time will equate to many times the predicted lifespan of the universe outside. It's hard to imagine something terminal wouldn't happen to the ship in that final second, assuming there's anywhere left for it to happen in.