The fact that they had to shut down a Youtube channel and got tons of complaints for daring to imply that PB & Marceline might have been a couple at one point leads me to believe that any relationship shown between the two from here on out is going to be inherently subtle and deeply in the closet as it were if they're gonna drop those hints.
I have my problems with the way that it came about seemingly as more pandering to fans than as a desire to write those characters as gay/bisexual, but I do sorta wish that they would have had the balls to run with it if they really wanted to go to there.
Ignoring the lame snipe at bronies, homosexual relationships aren't any more inherently sexual than heterosexual ones - no one looks at Finn/Fire Princess or Finn/PB or whatever they're spinning this week and thinks ew, gross, get that sex outta my cartoons!
I mean, whatever you think of the PB/Marceline thing, there's nothing that would make it automatically less "innocent" or more sexual than any of Finn's crushes on the show.