Either way I'd have to renumber everything. If I'm going to do that why wouldn't I just go straight to IPv6? I already have IPv6 on my home network (but everything has an IPv4 primary address and name resolution always resolves to IPv4); and an IPv6-supporting ISP. The question is if it's a good idea to go IPv6 only for some or all machines, and how to deal with the IPv4<->IPv6 issues.
If it's your home network, you could use 172.16.0.0/20, as well as the CGNAT /16.
> If I'm going to do that why wouldn't I just go straight to IPv6?
Because it is a lot more than just renumbering.
Whether or not it's a good idea depends on what you expect to get from it (anything?), how good your ISP's IPV6 support is, and how good the support of hosts you connect to is.
If whatever hosts you contact are all on IPV4 only, then you'll have to occasionally debug the 6to4/4to6/Teredo/whatever kludges that add latency and provide nothing of value compared to using an IPv4 directly.