Frankly, I think the intersection on the venn diagram of 'voted leave' and 'likely to vote labour' is pretty small. Plus the 'general electorate' didn't vote leave, it was roughly 1/3 did, 1/3 didn't, 1/3 didn't reply, so the large majority aren't actually leave voters. Opinion seems to be they're terrified they might lose votes to UKIP but their stance, it seems to me, will do little to attract those who were thinking of voting UKIP - frankly, if they're not going to vote UKIP they're going to vote Tory - while alienating those natural labour voters who were either remain or neutral.
Got nothing to do with the divisions in the party. This isn't some story leaked by a Progress member with the aim of sabotaging an otherwise popular Corbyn policy, this is Corbyn himself (IMO) completely misreading the opinion of the people in the party he's been relying on to keep him in office. It could backfire on him in a major way.
This is entirely separate to the argument as to whether triggering Article 50 and whatever the deal we get afterwards is good or bad for labour voters. As you say, Article 50 is going to be triggered. It's to do with whether a party represents the will of it's members. Corbyn got into office because he represented the will and opinion of more labour party members than Angela Eagle or Owen Smith did. If he forces through a major policy position in the exact opposite to the opinion of those same party members, he's asking for trouble. This isn't Corbyn & members vs PLP, this is purely Corbyn vs Members.