It was so sweet of those letters to try to reason through which ships were the most popular based off of who shares a book and who is married and who is canon when the reality is we live in a world where the Dr. Suessian character the Onceler was shipped with himself. The only logic one can apply is that anything can happen. It’s not a matter of if the on-paper folks have any chemistry, it’s what the subtext pulled out of an otherwise meaningless piece of dialogue can build into a memeable fervor.
Which, to that end, the most popular non-canon ships would obviously be Blake Washington Jr and Ra, The Prime Wardens as a polyamorous relationship, and Visionary and Dark Visionary. Facts are facts, folks.