Send feedback to Microsoft. Click in the search bar (upper right) and choose "Help improve Office?" to open the Feedback to Microsoft panel. This will bring you to the feedback portal for Word, where you can add your suggestion. Note that the portal is a bit confusing: it opens with the most upvoted suggestions, so old ones may appear at the top. Review a few to get a sense of how popular ones are structured: use the filters to see if there are any that may be similar to what you want to suggest. If so, add your comment; if not, create a new feedback. Either way, keep it simple, and there's no point in ranting.
Will they listen & act? Hard to know for sure, but over time I've noticed that suggestions have been taken into consideration for updates.
Edit: I just checked the portal and did a search on document tabs. There are several recent posts on this topic. Most show that Microsoft has changed the status to Open, so that's a good sign. Add your vote, and comment as applicable. Feedback on 'document tabs' feature.
