My thought is 50% Alain, 40% Tobias, and 10% Boz (possibly a smaller cut for Boz if Mike Farrell provides material). It makes sense that Jesse and Boz seem to be overriding Alain at this stage, since he's not in a position to rehearse with them. Think of the end of the YATQ tour: I'm Playing Easy To Get, Noise is the Best Revenge, and (on singles) The Public Image were all Boz's songs. (Slum Mums was co-written with Boz and Gaz.) Then, Alain wrote half of ROTT, seemingly against the odds.
My biases re: Alain have been well-known here, but, semi-objectively, I hope this ratio is the minimal amount as most of Tobias's material is incredibly ephemeral and samey to my ears. Given what we've heard thus far, Morrissey appears to be relying on Jesse for the singles, so I get the sense that Alain will provide deep album cuts that provide the affair with the needed gravitas. Boz is all over the map historically--it's hard to say what he will turn up with.
Cheers,
Jamie