Re: I can take a stab at it..
"1. Usability sucks"
Not true. Was maybe true 15 years ago.
"2. Massive capex required to replace incompatible kit"
Not true. You'll get IPv6 when you next update your kit anyway. That's why the preferred deployment is dual-stack, so you can run IPv4 as long as necessary.
Don't scare them with facts - when it comes to Ipv6, for some reason there are a bunch of detractors here who downvote without commenting, or provide no legitimate argument against it.
They just hate what they don't understand.
They are like the fox news/republicans of IPv6