If James stays out, and no other Democrats other than Juumane Williams runs, I'd probably pick Williams to win the primary, unless Hochul moves dramatically to the left.
She's in a very similar position to Kirsten Gillibrand in 2010, and she might not have the National Establishment backing her up, since Biden will be under pressure to stay out of the race, and the left wing of the party, especially AOC, will back Williams anyways.
Not convinced. Hochul would have very solid support in the suburbs in a one-on-one primary vs. Williams, and I don't think NYC alone is enough to win a statewide primary yet. She's also been sounding the right notes for a primary so far; despite her reputation as a centrist among the very highly politically engaged, I don't think the public sees her that way. Maybe Williams could start being competitive if he wins endorsements from some Upstate city politicians and can keep the margins down in the urban counties Upstate, but Hochul already has at least Buffalo locked up.