Here's an interesting excerpt from the Wikipedia article on ESPN+. It sounds like most folks who have ESPN3 via a subscription to a cable company's ESPN offerings won't have a great deal of incentive to also subscribe to ESPN+, unless they are fans of certain specific offerings, like CFL or Ivy League football.
"The service will focus primarily on overflow content similar to that of ESPN's existing digital service ESPN3 (which is distributed to subscribers of participating internet and television subscribers), though some of ESPN3's content will be shifted exclusively to ESPN+, such as most Canadian Football League coverage. Its launch content includes boxing (with exclusive US rights to the Amir Khan vs. Phil Lo Greco bout, as well as archive content from ESPN and Top Rank's libraries), college sports events (including Ivy League events, with the conference having reached a 10-year media rights deal with ESPN prior to the service's launch), the PGA Tour Live service, coverage of Tennis Grand Slams, as well as international cricket (Cricket Ireland and New Zealand Cricket), soccer (including the English Football League, Major League Soccer, UEFA Nations League, and the United Soccer League) and rugby events (including SANZAAR tournaments, Bledisloe Cup, Currie Cup, Major League Rugby, Mitre 10 Cup, and the World Rugby Sevens Series)."
Link to full article:
https://en.wikipedia.org/wiki/ESPN%2