Canal de communication privilégié pour l'accessibilité pour les lecteurs aveugles ?

Yep! that’s why the email address exists — everyone on our team can access it.

Linking someone directly to the signup, for example meta.discourse.org/signup may help… any suggestions for improving the current account creation form would be welcome (what would a dedicated accessibility oriented signup form change ideally?)

Yes it’s possible, but must be configured per-category or per-group, there’s a guide here: