[Decade]

Not essentially what we have with IPv4.

IPv4 is from the old days of 1 device, 1 IP address.

RFC 4193 addresses are in addition to the globally routable IP addresses. Your laptop could have both classes of addresses. Your printer could have only one class of address.

Between the ULA and the global addresses, with DHCPv6 and NDP and IPv6 privacy extensions, my laptop currently has 13 IP addresses on its main network adapter. That’s leaving my router and my laptop on default settings, nothing special, no appreciable memory impact.