As a new e-Tron owner in the LA area, I have not been to Vegas yet. But I did speak with a Bolt owner who has done it and ended up having to wait 1hr in Baker for someone to finish charging, then an additional hour for her Bolt to charge. She said she would not take her Bolt to Vegas again. From what I see, there are not enough DC chargers out there and from what is out there, most are 24-50Kw. at 50Kw, an e-Tron should take 50-60 minutes. Ugh! Only Electrify America seems to be installing 50, 150 & 350 stations. 150Kw should be in the 2-30 minute range.
PlugShare is a great app. I've set mine to only view DC charging stations. But you cannot see the Kw, unless you get the App for that vendor.
https://abetterrouteplanner.com is an AWESOME map with charging stations. For my specs, I updated the ambeint temp and e-Tron consumption specs to simulate what I may really need.
For the Electrify America "coming soon", within the app, you can choose to notify you when the station is operational. From what I've heard, the "coming soon" sites should be complete by end of 2019.