Based on my one experience as well as some of the reports in this thread (e.g., this one, this one, this one, this one, this one, this one, and this one) I don't believe this is true. It absolutely still appears to be hit or miss, but based on the anecdotal evidence in this thread I believe there will be more hits than there were previously.

In the past month I've also seemed to have gotten some solid upgrades on non-UC rentals at airport locations (QX80 on an L4 reservation at DTW and a fully-loaded Buick SUV (whatever that Chinese made one is) on a mid-size reservation at LGA), but maybe that's just a small bit of good luck.