The best thing about SLAAC is that it forces your ISP to give you at least 64 bits. Otherwise you know Comcast would only give out a /128 and charge you for more, so you'd use NAT at home just like IPv4.

Unfortunately SLAAC doesn't force upstream to provide a /64 universally.

Some ISPs are reportedly giving out a /128, and SLAAC works adequately with a router performing IPv6 NAT, so those ISPs don't see a problem.

Mobile phone as WiFi access point is another common way people access the net nowadays. I've occasionally seen permanent installations, with a phone taped to a window. I've never seen a mobile phone AP offer IPv6 to clients, but if they do they have to use SLAAC-compatible IPv6 NAT in that situation.

Thats why android supports dhcpv6-pd for a /64, but not assigning a /128 from dhcpv6

Well, my phone as access point grants an IPv6 public IP without NAT. There's a stateful firewall somewhere in the chain though.