"if you want to spend time learning about IPv4 right before IPv6 becomes the dominant standard"
Not as much is changing as you think, at least for basic concepts and intro level stuff. Simpler in some ways.
To kick over a real bee hive, as I guy who's used ipv6 for I donno a decade or so now, the main issues are NAT6 love it (noobs) or hate it (folks who know what they're doing), believe it or not its easier to make a statefull firewall than to do NAT, some folks have bizarre ideas about ipv6 netmasks and what other people should be permitted to have, the concept of RFC1918 in ipv6 is more complicated, router advertisements RA love them or filter them, you probably need DHCPv6 or maybe not, and some firewall nuts filter DNS traffic into packets too small to hold AAAA records (but large enough to hold A records) Other than that ipv6 is just obese ipv4, the concepts of subnet and mask aren't changing, you've still got ARP just different address family in the protocol...
(edited to add my favorite topic, hand editing text zone files is probably not the most scalable way to implement reverse (or forward!) DNS for ipv6 from pure PITA perspective. Then again doing things by hand instead of automating is a PITA for ipv4 not just ipv6.)
Not as much is changing as you think, at least for basic concepts and intro level stuff. Simpler in some ways.
To kick over a real bee hive, as I guy who's used ipv6 for I donno a decade or so now, the main issues are NAT6 love it (noobs) or hate it (folks who know what they're doing), believe it or not its easier to make a statefull firewall than to do NAT, some folks have bizarre ideas about ipv6 netmasks and what other people should be permitted to have, the concept of RFC1918 in ipv6 is more complicated, router advertisements RA love them or filter them, you probably need DHCPv6 or maybe not, and some firewall nuts filter DNS traffic into packets too small to hold AAAA records (but large enough to hold A records) Other than that ipv6 is just obese ipv4, the concepts of subnet and mask aren't changing, you've still got ARP just different address family in the protocol...
(edited to add my favorite topic, hand editing text zone files is probably not the most scalable way to implement reverse (or forward!) DNS for ipv6 from pure PITA perspective. Then again doing things by hand instead of automating is a PITA for ipv4 not just ipv6.)