Yeah, the network admin costs don't double, they're marginally larger.
> ...you can't fearlessly combine/add routes between any two subnets that you have.
You can't do this with ULA subnets, either. The standard way to do ULA subnet calculation is collision-resistant, not collision-proof. There's NO central coordinating body to prevent collisions. While the odds of collision are VERY, very low, they're not zero.
The benefit is that you pretty much never have to renumber after network merges... it's NOT that you never have to check for collisions.
> To my mind the key benefit of using IPv6 ... is to stop having to worry about address assignment and address collisions and local addresses...
See above.
> ...if you can't get away from having to give all your hosts individual v4 addresses and keep track of them then frankly you might as well just stay v4-only...
This is nutty. If you don't get why Internet-connected systems configured with "NATted IPv4 + globally-reachable IPv6" is strictly better than "NATted IPv4 and no IPv6", I question how deeply you've thought about this.
> ...it sounded like you were talking about using a mix of v4 and v6 within the VPC...
Yeah, the network admin costs don't double, they're marginally larger.
> ...you can't fearlessly combine/add routes between any two subnets that you have.
You can't do this with ULA subnets, either. The standard way to do ULA subnet calculation is collision-resistant, not collision-proof. There's NO central coordinating body to prevent collisions. While the odds of collision are VERY, very low, they're not zero.
The benefit is that you pretty much never have to renumber after network merges... it's NOT that you never have to check for collisions.
> To my mind the key benefit of using IPv6 ... is to stop having to worry about address assignment and address collisions and local addresses...
See above.
> ...if you can't get away from having to give all your hosts individual v4 addresses and keep track of them then frankly you might as well just stay v4-only...
This is nutty. If you don't get why Internet-connected systems configured with "NATted IPv4 + globally-reachable IPv6" is strictly better than "NATted IPv4 and no IPv6", I question how deeply you've thought about this.
> ...it sounded like you were talking about using a mix of v4 and v6 within the VPC...
Yep. See above.