I mean, I saw a ton of art of the new PowerPuff girl Bliss too, and honestly this isn't even on that level of popularity. It's a new design that has a vague Miku Hatsune type of appeal, but not quite to that level, and the character herself doesn't seem very interesting so far. I don't think most classic of nu Joker fans really want him to have a girlfriend, outside of a few self-inserting fangirls, and they were about Heath Joker or now Pheonix Joker, not the comic book Joker.
Punchline could become a character people like with good writing, but if she's just a generic asian girl with knives she'll be less than a flash in the pan. Outside of the /co/ shilling from a few anons, I can count on a hand or two the cosplay/art I see of her much less that's getting any traction. Smug Wendy (the fast food one) was a million times bigger than this, probably because she had a hook.
I don't think it has anything to do with Harleyfags, but the opposite, in that people might pay attention to her if she's hyped as "the new Harley." There's nothing there yet.
And original Joker fans never liked that they gave the Joker a girlfriend in the first place as they thought that diminished him as a character.