I don't think the constitutional hurdles to moving on this are insurmountable in any way. I could be wrong; the courts are not entirely predictable on this.
I would go back to a point I made earlier, that the courts are constrained to a degree on this by the nature of the question they would be forced to address. The design of representative institutions is not really a comfortable territory for the courts.
If the courts were faced with a challenge in which they would be forced to either stick to the black letter of the law of something written 141 years ago and block the democratization of the Senate, or provide some latitude, I think they would provide that latitude. But I don't know. However, it seems to me it's not a foolhardy path to follow on this. It does force the issue, there's no question about that.