So, I'm working with actor/writer/producer Chas Burns for bring one of my books to the Audible market. Through ACX it's a relatively simple process. Post your project, readers audition, choose the one you prefer, agree a contract and off you go. Simples. I forwarded the manuscript to Chas, he sent me a sample, I loved it (tear in the eye, it was that good). Too late now to do anything about it, but...
Seems to me that a different style of writing is required for an audio book that has yet to be invented. A cross between the traditional novel form and a screenplay. Or at least a light adaption. All those 'he saids/she saids' seem clunky and unnatural from a modern perspective. Two points arising [1] you can easily get away without attributions, or at least minimal attributions, when writing dialogue. [2] in natural modern speech, 'he said/she said' is falling into disuse in favour of less formal/stilted terms e.g. 'he's like/she's like.' Strikes me that a radio script style of writing would suit audiobooks best. For all I know adaptions to such a format may already be in use.
So much depends on the style/quality/versatility of the reader. If all the characters in the dialog are voiced similarly, then attributions are essential. If the voice artist gives each a distinctively different intonation or, at best, voice character, then attributions are unnecessary and disrupt the flow of the narrative. Depends essentially on the ambition of the writer. Whether they want the narrator to tell a story, act a story, or simply read a book.