I picked up last night at AUS for a one-way rental. When I first arrived at the lot, the Presidents Circle area had two 2017 Maximas, a Hyundai Sonata, a Ford Escape, and a Jeep Grand Cherokee Limited. I initially picked the Jeep, but after going on a mini-tour of the new facility, I came back to find a VW CC that had been deposited, so I snagged it.
The rep inside told me Wednesdays were the worst days for selection (no surprise--middle of the business travel week) and weekends had a sea of cars to choose from. A PC friend picked up at AUS last Saturday and said there were lots of options, including an Infiniti Q50.
I didn't get a traditional Carfirmation text+email; instead about 1.5 hours before my reservation, I got an email (no text) telling me to go to the PC area with a map of the lot attached.
I walked the lot and didn't see anything more appealing in any of the other areas (midsize, like I'd reserved, or the Gold/5* area) so didn't test the waters about picking up from one of those areas. The "Premium/Luxury" area had 4 Infiniti Q50s, 2 Chrysler 300s, 2 Infiniti QX60s, and one Mercedes C300. A sign next to the area said that upgrades were available to these vehicles for $35/day. The wording on the sign is that it is a fixed $35/day for any of those vehicles, not a "from $35 and up" type of thing. I was tempted by the Merc for $35 and may have done it if the CC hadn't shown up. (I'm sure the fleet management would have loved me taking a Merc out of their fleet, ha...or maybe the offer isn't available on one-way rentals. Would be interesting to test sometime.)
There were other areas labeled "midsize" and "fullsize" but no other areas for premium or luxury cars, so it almost looks like anyone with a premium car reservation can pick up from the premium/luxury area (and there isn't anything there that differentiates a premium from a luxury). However, a friend who rented last week on a PCAR reservation was assigned a specific vehicle and parking stall with his Carfirmation (a 2017 Maxima, so most definitely not an Infiniti or Merc!), so maybe the "choose your own car" thing actually doesn't work with PCAR/LCAR reservations. FWIW, I also didn't see any areas labeled for "Standard" cars, only compact, midsize, and fullsize, so I don't know what would happen with an SCAR--or, for that matter, ECAR--reservation. The 5* area is the same as the Gold area, so I don't know how the 5* upgrade benefit is handled; that said, the Gold/5* area actually had several cars larger than midsize (Sonatas, Malibus, etc.), so apparently Golds get access to the same upgrade inventory as 5*, I guess. Odd.
Either way, not bad at all for a midsize rate and way better than the 50K-mile Corolla or 200 they would have tried to foist on me in the old days for a one-way res.

As this rolls out to more locations, this appears to finally be making the Hertz experience competitive with National (though National's rewards program remains superior, IMO).
ETA: I just noticed that this line was in my Ultimate Choice welcome email:
Originally Posted by Hertz Email
As a President's Circle member, you may also choose from the Five Star | Gold, Fullsize, Midsize or Compact sections of our lot, if you prefer.
So it seems that it's legit to choose from those other sections if there's something else you prefer to drive.
Also, I'm still somewhat curious how PCAR rentals are handled. I suspect it's as my friend experienced and you get a specific stall reserved. If so, I think that calling the upgrade area the "Premium/Luxury" area is misleading. I think it would be much clearer for them to label it "Prestige Series Upgrades" (since
that's what the Hertz website advertises the upgrade area as being) and then have a Premium and Luxury area for people who booked those classes to choose from. JMHO.