I get most of your points but from experience it just doesn't work out very well. For example I get a different /64 (or was it /60?) prefix every day from my ISP. I complained about it and the reply was that they don't offer a stable prefix for non-business customer. Your point with email is something I didn't experience. I could never get email on ipv6 only to work because the mailservers I wanted to send mail to were ipv4 only...