the 'dotted quad' format was 'good enough' from a UI perspective (and... fitting in peoples' brains for short term). had we added one or two more spaces - and default all existing addresses to 0.0.x.x.x.x, we'd have had 65000 more blocks of 4 gig spaces. That should have been enough for most countries to have allocated enough space, while making the transition and UI upgrades pretty painless. If there's only a x.x.x.x address, assume leading zeros, and so on.

it's "failing" for a number of reasons - the UI and mental map model is certainly a stumbling block, but it's also something which requires coordinated effort between multiple parties to happen more or less at the same time. If it doesn't (and it didn't), it'll take years more for all players to get in sync, which is what we're seeing.

Residential ISP companies didn't have much incentive to upgrade when everyone's OS didn't include IPv6 stack. Not much push to try to upgrade your OS when your modem and ISP don't support it. Not much use to try to support it on your websites and email servers when no one is using it or asking for it.... and so on.

As all the pieces fall in to place - hardware, ISP, OS, web/mail/services - it'll still be a gradual move, unless some major players announce IPv6 only service. If Office365 was "IPv6 only in 2020", that might motivate a lot of orgs to push their IT/ISP to upgrade and migrate.