and that's what will be used by default, in the new version, to handle any other file type
You mean the new version of the web interface?
Current PDFe document handling is fine - Sumatra as a internal viewer covers all the most popular file types. To start fully appreciating it we only need to get more file types listed in the grid.
The thumbnail idea for PDFe is a different topic though. We will need to collaborate on this later.
For your scenario it's probably better to, a least, add the file reference to the grid.
But what if I want only to open a temporary document? For example, that which shows the resulting document but, for a better preview, as a handout, or as a report log? Do I really must to include it to the grid just to have it removed (manually?) after checking it? This seems too restricting.