As a customer I'd like to see a Netflix/Spotify-like audiobook service, where I pay a subscription and can listen whatever they have in catalogue, whenever.

Sadly, it wouldn't probably be great for small authors either, just the same as Spotify isn't great for unknown musicians. OTOH, like Netflix, they could fund authors to write books or at least produce the audiobooks for them. Of course the service would want exclusivity, but perhaps it might work out.