It's a simple toggle on vs asking orgs to redo their entire network. In both cases you need routers and network stacks to support the new packet format, but that isn't the hard part of ipv6, we already got there and people still aren't switching.
Sorry, I'm still not seeing how a IPv4+ would be any less complicated (or as simple) as IPv6. In either case you would still have to:
* roll out new code everywhere
* enable the protocol on your routers
* get address block(s) assigned to you
* put those blocks into BGP
* enable the protocol on middleware boxes
* have translation boxes for new-protocol hosts talk to old-protocol-only hosts
* enable the protocol on end hosts
And just because you do it, does not mean anyone else would do in the same timeframe (or ever). You're back in the chicken-and-egg of whether servers/services do it first ("where are the clients?"), or end-devices ("where are the services?").
Redo all your addresses and routes, reconfigure or replace NAT and DHCP, reconfigure firewall, change your DNS entries at minimum. If it's a home or small business and you don't want to fight the defaults, you go from NAT to NATless.
