Thanks for alerting me, indirectly, to the Spival pronouns. I think they're a good, minimalist approach to a fix, but agree they will look distracting until or unless they become commonplace.
I guessed - correctly - it would be the same Spivak who wrote the excellent Calculus textbook.
"They" as a gender neutral singular pronoun is, to me, perfectly natural. I use it dozens of times a day as such without noticing.
Spivak pronouns, on the other hand, are blatantly marked, and were I to come across them in writing or speech, I'd find them very distracting.