<quote>DNS unambiguously defines A records as exactly 32-bits. Hence the existence of 'AAAA' records</quote>
For the proposal at hand, which as I understand it is to extend the IPv4 address space by 16 bits on the right, an 'AA' record will do and only needs to be implemented at the edges of the classic IPv4 space. In other words, at points under complete control of participants in the experiment.
An 'AA' record would sensibly be defined with the classic IPv4 space in the middle four bytes, the IPv4++ bytes on the right, and the two remaining bytes on the left reserved for future expansion.