Hi @juniorgerdet, welcome to the Supernotes Community 
First off, love the format of your feature request, very thought through. Offering ‘full-width’ cards is something we’ve been considering for a while. However, the reason we’ve not added this yet is because it slightly goes against the ethos and vision of the short-form format of Supernotes.
Offering a full-width mode encourages to do as exactly as you said write more detailed notes – creating longer content and content that won’t work well on a small screen, such as large markdown tables. By limiting the width, we encourage you to break down your ideas into smaller pieces, and ensures that it will look great on whichever screen your reading your notes on.
That’s also the main driving factor behind using the Broadsheet view over the List view.
Having said this, we still want to tackle all of those three benefits you’ve mentioned, and believe that a distraction-free mode, where you can see one card at a time (not full-width but with a larger font) will be a more optimal solution. This could be a toggled mode within preview so you can either view the preview as a card or in this distraction free mode.
Food for thought, it’s on our minds and we’ll improve this soon. If you have any further comments / suggestions please let us know down below 