The v6 addresses are made up of the network prefix (2001:db8:2d4f, basically an opaque string like 203.0.113.45+192.168), then the subnet ID (1, 2) and then the host ID on the network (1-3 and 1).
When you look at 2001:db8:2d4f:X::Y, it should be pretty easy to see that it's host Y on subnet X, under your prefix which is the same for your whole network. Even if it's 2001:db8:2d4f:X:YYYY:YYYY:YYYY:YYYY it's still the same thing, just with more characters.
The most common is more like /56, which is unfortunate because it means you have to deal with "2001:db8:2d4f:61XX::". It's still easy enough to read the subnet out of :6101:, :6102:, :6103: etc, but it does mean every address is longer :(
> And has the practice of generating portions of the address from your MAC address been universally (or at least mostly) abandoned?
Somewhere around mostly. Windows, OSX, and network-manager/dhcpcd/systemd-networkd on Linux all enable RFC7217 (uses a hash of your MAC and a secret value), temporary addresses (random addresses used for outbound connections) or both by default. Either of these will prevent people from seeing your MAC when you connect to them.
I'm not sure about mobile devices. I'd expect temporary addresses there, but also MAC randomization is a thing these days which would do the job too.
Notably absent from that list is Linux's in-kernel SLAAC client. Client-oriented distros often enable tempaddrs by default (or they install one of the network daemons that does it), but server-oriented distros tend not to.
Here's some roughly equivalent IP addresses:
The v6 addresses are made up of the network prefix (2001:db8:2d4f, basically an opaque string like 203.0.113.45+192.168), then the subnet ID (1, 2) and then the host ID on the network (1-3 and 1).When you look at 2001:db8:2d4f:X::Y, it should be pretty easy to see that it's host Y on subnet X, under your prefix which is the same for your whole network. Even if it's 2001:db8:2d4f:X:YYYY:YYYY:YYYY:YYYY it's still the same thing, just with more characters.