Stats+CS at UIUC has been around for a while.
BTW, as a Stats+CS major at UIUC, you’d already be a CS major (you’d take the same core classes that all CS majors take, and while CS electives aren’t required, you may take those as well), so there’s no way to “transfer in to CS” as the CS department would already consider you a CS major. However, it’s extremely difficult for non-CS students to transfer in to any of the CS majors (CS in Eng, Math+CS, Stats+CS, and CS+X) at UIUC anyway.
They’re both good schools for CS, BTW. You should probably make the decision based on fit (or the non-CS courses you’d have to take, like stats in Stats+CS).