I'm also doubtful the public will is there in the UK, either. I wish I could say with confidence that if we had another referendum tomorrow on whether to rejoin or stay out, rejoin would comfortably win but I can't. It's one of those things which seems so obvious if you support one side, you just can't see how the other can possibly take the position they do.
In respect of the site, it's not going to persuade anyone who was either in favour of Brexit or on the fence, is it? It's clearly designed to preach to the choir. But partisanship and ideological bubbles is how we ended up in such a mess in the first place. If any campaign is serious about rejoining, they need to accept two things, IMO - first, that it's a generational cause, not something which will be achieved within a few years, and second, that any campaign will only succeed by making concessions with the EU and the pro-Brexit faction among the public, by understanding them and by forming a new relationship. To call this task gargantuan is an understatement.