One happy result of working on abba is that it's informed my understanding of the Abbreviations, too. One immediate and obvious consequence is that it will force me to very rigorously define positioning rules and such; any place where I've been allowing myself to fudge things a little when composing texts—because things will be immediately obvious from context—will be exposed, and the abba implementation of the New Abbreviations will evolve as a reference implementation of the Abbreviations themselves.
Something else that this has pointed out to me is that the unicode realization of any given abbreviation and my handwritten realization of that abbreviation need not be very similar at all. Precisely because abbreviations are objects, with multiple renderings, before they are unicode characters, means that I can happily say that 'in', for instance, can look like 'ɹ' in unicode and look like something similar, but distinct, when written by hand. And if I want to write a bitmap outputter or something that replicates the glyphs as they're written by hand at a later date, I can.