It absolutely is a showstopper if you don't have applications that are NAT friendly. And in 2016 if you are forcing people to use NAT and claiming that's a fix, you're doing the entire world a disservice.
I've been hearing this argument for 15 years now and it hasn't changed. Sure, there's a public address shortage these days, but the incessant whining by end-to-end purists who think NAT is an unbearable sin falls on deaf ears just as much now as it ever did.
I'm not against V6 by any means, but internal IPv4 private subnets are simply not a problem for the 99+% of who still somehow manage to get things done in the real world.