This will be an inherently risky move, but I did see a poll from ComRes on the European Parliament elections that Labour would increase its vote share by 12 points if it came out as a pro-Remain party, though of course such polls need to be taken with grain of salt. I've ran out of patience with Brexit and feel there's no form of Brexit Labour can offer that will please Leavers. No road left except one that leads to the end: a no deal Brexit.
I feel it would be better if Labour avoided another referendum and instead forced a general election, and then campaigned to revoke Article 50 if it got into power. That's really the only altenative now to a no-deal Brexit. The window to get a good Brexit deal had been missed. Of course, this will drive away Labour leave voters, but it seems they're already migrating to Nigel Farage's new Brexit Party, being angered by Labour flirting with the notion of another public vote.