I think generally the meaning of what and how in these sentences can be interchangeable. 'What about you' and 'How about you' both express interest in knowing someone's opinion/ the way someone is feeling. The difference may lie in the preceding part of the discourse, so that if someone starts with 'What' the logical consequence is using 'What' and if someone starts with 'How' the logical consequence is using 'How'. In spoken language these lines are obviously blurred and depend also on the habit of use of the speakers!