Personally i can see why Gillian Welch and Amos Lee is in the same radio stream just by looking at the genres they share though not Americana and Jazz respectively. I have tracks from both sharing the same Tag for play from Bookmark/Focus but then hand-picked tracks.
In case of total overhaul of Roon Radio i would propose to build a solution around Focus by adapting Focus to also include non-library tracks in addition to library. In this way each user can prepare it’s own Radio Stations by creating bookmarks as the seed. In future versions additional features could be added like the option to adapt the bookmark/seed as You listen by giving the user the possibility to add or inhibit the actual artist that is playing to the bookmark/seed from the queue screen.
Another feature that could be added later is for the user to decide to what extend this Radio should “play safe” or be adventurous compared to what is defined in the seed. That could be portion of (non) Loved/Library stuff, stick to Genre stricly (or not), etc.
I think that a solution using Focus would adress both the different preferences of the Roon users and also @Suedkiez point that the same user may have different idea of what Radio shall provide for each session started.
// 1: Radio as playlist
Radio can also be a playlist with X tracks created from the Bookmark/Seed up front. This playlist can then be added to the queue or replace it similar to how adding to que is handled today. Both Spotify (last time i used it) and Tidal has pre-prepared playlists for what they define as Artist Radio’s.
// 2: List banned non-library stuff
Extension of Focus to include non-library stuff would also solve the request to be able to see what is banned outside of library.
// 3: Thumb Up/Down , Skip
The thumb’s handling, as commented by @ravyn and @Paul_Melde should also be evaluated. These has never been intuituve and often misunderstood since it does now follow defacto industry standard. Now after the introduction of Ban in addition to Love it is even more confusing. If Focus/bookmark and pre-generated playlist they will have no function related to the actual stream/session.
From my understanding the feedback given after thumb down/skip (This doesn’t fit / Holiday music / Not for Radio / etc ) does not add to the users Radio/profile directly and has little or no effect on what will be played later in the actual radio stream or later radio sessions for the actual user/profile.
// 4: Possibility to hide
Depending on the implementation the option to hide menues, buttons etc related to Radio/Ban/Focus-extensions should be considered.
// 5: Usability of personalized Radio and Daily Mix’es
To ease the use of own Radio (chosen) Focus-Bookmarks could be put on the Home page similar to how the Daily Mixes are shown today or even replace today’s mixes based upon user decision. Possibility to add own graphic to each Radio-Station/Bookmark would have been nice.
In general home screen should be adaptable and could also include the most used playlists for the actual user-profile, also with own graphics … 
& the option to add “last played” filtering/sorting and shuffle to have fresh music every day even from own static playlists. This could also sync with Arc and download to refresh.
An adaptable personalized Home page would also play into the overall user experience of Roon as a Music Player that presents Your music as a Magazine.
// 6: Sonic analysis
Considering adding the option to do Sonic analysis of the tracks to be able to match them for Radio/Playlists. I have Bookmarks for both “Late Night” and “Training/Work-Out” music . They are very different but can include the same artists and genres. Plex and Pandora has this feature.
MusicIP/Spicefly has similar features , found this in tread started by @armandhammer in 2020. I believe this was integrated into Spotify as MusicMatch in the early years. Roon does not have to develope all features themselves if available from a proven trusted supplier.
// 7: Use of AI
Make use of AI for later-later releases if/when more mature and resources available.
I have a few playlists in Roon today for discovery music/genre’s that is AI generated from Soundiiz to Tidal and Qobuz. The generation of these would be improved if the rules could include to avoding stuff i already have in my library and enable user interaction on the fly to adapt the source/seed/text.
Edit:
// 9: Library vs Non-Library tracks in Radio
It would be nice to have the option to decide if Radio (and Daily Mixes) should prioritize the (i) track from library or ii) track with highest quality independent of location.
/Edit
==> Einar needs to stop now …
Figure below shows example with Focus for the use case above with Gillian Welch as seed where i have added, (i) last played, (ii) artist not to be played, (iii) genre and (iv) releases from 2000 onwards. The latter just to save the classics of the John’s (Hiatt, Prine and Cash) for another radio dedicated to “old favorites”.
