I'll keep this topic open until it's implemented.

The mockup does look nice, but you have to keep in mind that the current design is already tall for some users (mainly laptop users it seems).
It would work for me, but I have a 49" 5K screen 🤣 anf not everybody has this.

I've added this as a feature request on my to-do list, maybe I can make it an option in the Preferences with a next release.
This way users can toggle between banner (default) and poster (optional).

Not sure when a next release will be made available, I usually try to collect a few requests at a time, since each release takes quite a bit of effort and time to do (releases for Windows, MacOS, Linux QT5 and Linux GTK).
I'll post the update in the comments and will try to remember to post it here as well.

😊 

Having said that, the Poster can be downloaded automatically (even though this will not be helpful for your situation):

Since there is no poster for each episode, checking the option below will place the poster, banner etc in the parent directory of the directory where your episode file is saved in.

In case you do not want this (understandably so), you could check the preferences / Application Support directory. 
Obviously less convenient, but maybe helpful?
The files are typically named: <provider>-<providerid>-post.jpg, eg. "TVDB-420415-poster.jpg"
You can click the "Copy <provider> ID" button in the lower left corner to copy the ID (I've added to the To-Do list to make that ID visible in the future to make that easier).

Mac:

/Users/<username>/Library/Application Support/Rename My TV Series 

Linux:

~/.config/Rename My TV Series

Windows:

c:\Users\<username>\AppData\Local\Rename My TV Series

Apologies that I do not have a more convenient way of doing this.

@hans Hi friend, I understand what you mean, but look, I made this example of how it would look, and honestly I do not think it would be too large. On the contrary, I feel it looks quite good and gives Rename My TV Series 2 a very professional touch. Personally, I really like how it looks.

Also, as I mentioned before, something like this would make it much easier to identify series and movies. I have already come across several that do not have a banner, and I have to go to TVDB to confirm whether it is actually the series or movie I am looking for. Instead, if it could be recognized directly by the main poster inside Rename My TV Series 2, it would be much more practical and convenient.

Having said that, the Poster can be downloaded automatically (even though this will not be helpful for your situation):

Since there is no poster for each episode, checking the option below will place the poster, banner etc in the parent directory of the directory where your episode file is saved in.

In case you do not want this (understandably so), you could check the preferences / Application Support directory. 
Obviously less convenient, but maybe helpful?
The files are typically named: <provider>-<providerid>-post.jpg, eg. "TVDB-420415-poster.jpg"
You can click the "Copy <provider> ID" button in the lower left corner to copy the ID (I've added to the To-Do list to make that ID visible in the future to make that easier).

Mac:

/Users/<username>/Library/Application Support/Rename My TV Series 

Linux:

~/.config/Rename My TV Series

Windows:

c:\Users\<username>\AppData\Local\Rename My TV Series

Apologies that I do not have a more convenient way of doing this.

open /System/Library/PreferencePanes/Keyboard.prefPane

or

open -b com.apple.systempreferences /System/Library/PreferencePanes/Keyboard.prefPane

 Is this what you were looking for?