They actually do have a web player. If you log in and go to your library, there's a "listen now" button next to your audiobooks. Selecting this will launch the web player in a separate window. With (what I imagine would be) minimal tweaks, it should be relatively easy to add this to Player. It would certainly be a nice and useful feature, in my opinion!

Here's a link to an article on their site detailing the feature:

https://help.audible.com/s/article/what-is-the-audible-cloud-player?language=en_US