> All that probability shorthand can be unambiguously translated to formal definitions quite easily. But doing so would be analogous to writing a complex program in assembly

One possible interpretation (probably, in retrospect, the right one) is that he meant that Whitehead/Russell style axiomatization of probability was in theory possible, but would not be of much value.

I read it initially (likely wrongly in retrospect) as saying that translating the equations into an unambiguous formal computer readable definition would be intractable and/or only of theoretical interest.