That .1 change has __all__ of the same (and maybe a bit more) problems as the move to v6.
(Because it makes things even more complicated, now you'll have not two incompatible but about three things.)
And of course the problem is/was of economics. No incentive to change, v4 is good enough for now, for the incumbents. And even if large companies with new users were running out of v4, they can afford trading netblocks and/or carrier grade NAT devices, both are cheaper than telling others to upgrade (and you'd lose customers/subscribers otherwise).
(Because it makes things even more complicated, now you'll have not two incompatible but about three things.)
And of course the problem is/was of economics. No incentive to change, v4 is good enough for now, for the incumbents. And even if large companies with new users were running out of v4, they can afford trading netblocks and/or carrier grade NAT devices, both are cheaper than telling others to upgrade (and you'd lose customers/subscribers otherwise).