The speed stat is lower, the rest were the same when I checked (briefly). Maybe it has more downforce or something?
Edit: using the magic of remote desktop I had another look while on my lunch break. The old Hoonicorn is 0.3 faster on the garage stats and its 1st gear ratio is 2.65 vs the Newnicorn's 2.60. I didn't check the suspension or brake settings but downforce and diff settings are the same, same power, torque, weight, weight distribution and PI too, so it's just a reskin with a mysterious but negligible difference in speed.
Maybe the mastery trees are at least different, I can't be bothered to log back in though.