I think the main issue I have, and likely many others too, is how strongly it is phrased. If he thinks he'll die in the next 5 or 10 years... fine, I guess? But that's unlikely, and with how things have shifted just in the past 25 years, making a statement like this seems arrogant.
Is that overanalysing a one line answer to a question? Probably, but that's what a politician gets and the effect of modern media.
Not to mention how the population and especially Labour supporters have turned pro-EU so he'll likely alienate that part of his base. Strong stances are seen as better, but I really feel sometimes he should take a softer approach.
Yeah, I don't think that coalition situation is likely to happen. Under FPTP, it's too risky for the voters to try manufacture.
That said, if their popularity massively tanks and polls show they'd lose big, I could see Labour introducing it just before the next election. It would be a huge boost to their popularity.