Had IPv6 been an incremental improvement over IPv4, with a larger address space, the costs would have been much less
This is not clear to me. It seems like the base cost of adopting any new protocol is pretty high, so simplifying IPv6 wouldn't have reduced the transition cost much. Given the high base cost, it actually makes sense to pack in as many fixes as possible IMO, especially since this is our one chance for the next ~25 years or so. (Some people are complaining that IPv6 didn't solve enough problems, like routing scalability.)
This is not clear to me. It seems like the base cost of adopting any new protocol is pretty high, so simplifying IPv6 wouldn't have reduced the transition cost much. Given the high base cost, it actually makes sense to pack in as many fixes as possible IMO, especially since this is our one chance for the next ~25 years or so. (Some people are complaining that IPv6 didn't solve enough problems, like routing scalability.)