my immediate thought when i think about like, "experimental pop" is The Hyperpop Girlies. SOPHIE, 100 gecs, ecco2k, etc.
nelward, jack stauber, neil cicierega (both the stuff released under his legal name & the stuff he releases under the lemon demon project,) hemlocke springs, dorian electra, and studio killers are all artists i think are doing cool stuff with the pop genre, too.
i agree though - i think hearing lady gaga on the radio as a preteen was the first time i remember being surprised by a pop song. especially for something that got a lot of radio play.