I'm not paying for it, but I think it will (unfortunately) do well for them. The goal isn't to get new people into the comparatively obscure programming it has but instead just to make money on those people who are already into those sports. They probably could have done this years ago rather than offering so much free stuff on ESPN3/WatchESPN for so long, though of course the idea is to get the people who took advantage of it to now pay up.
I also get the sense that they got pretty good deals on a lot of the sports they've been adding to it. They just picked up rights to a lot of European football in the last few weeks for extremely cheap, and if I ever wanted to stream legally I could see myself being a lot more inclined to pay for ESPN+ programming over the far pricier streaming services that NBC Sports and Turner are offering for the leagues they have the rights to (
here's good recent article about how expensive following all the leagues can become).