A couple of Simple Features

There’s already two suggestions addressing both aspects of your suggestion.

There’s already an existing suggestion discussing that option.

You can already do that in Plexamp (setting alternative rating schemes, built on the existing server setup, specifically: 5-star rating, 10-star rating, 1-star rating/like).
You can filter by unrated tracks using an advanced filter – it’s a bit tricky in Plex Web, because of how the UI handles no-rating vs. no selection, to overcome this, you need to click very close to the left of the most-left star (there should also be a suggestion discussing this). On the iOS app, there’s a dedicated “unrated” option but no option to create an advanced filter.

There’s an existing suggestion discussing this option in general → Music: Thumbsup/Thumbsdown

Not sure, what exactly you mean. Do you mean an option to apply a set of theme colors like on the Apple TV or other big screen apps?

Local extras added to your library will already show up in the iOS app for both movies and shows (incl. season and episode extras!)

You can already do that using Plex Dash (separate app).

There’s already an existing suggestion for this → iOS/iPadOS 15 widget support for Plex app

Please comment/vote in those existing threads in order to help us avoid distracting or cannibalizing votes.
As a side note – please don’t create compilations of suggestions in a single thread. This way, users can only vote for the full package which is significantly decreasing your chances of finding others to support what you want.