Sure, the bar appeals to kids and adults, but a key thing worth mentioning is how many more adults without kids are going to the parks. Having a few things (in MK's case, one) that appeal to adults more than kids in a park overwhelmingly geared towards kids isn't a bad thing. With the 45 minute time limit, I doubt we'll see people get sloshed like at Epcot.
Is it really so bad that there's alcohol in the pirate bar? There's non-alcoholic drinks and foods too, on top of the animatronics and show scenes, so it's not like kids get nothing out of it. It doesn't need to be 100% for kids, pretty much everything else in the park save Haunted Mansion and Tron is 100% for kids.