Since my graphics knowledge is dated at best, would switching to webp from jpeg have a negative effect on combining the multitude of separate updates into one game at the end of DMD?
If Mr.Dots plans to release DMD as a single unit.
If we're thinking about a combination of all chapters into one ... that will be quite a large package, I suspect! Regardless of which image formats are chosen.
But if things go that way, the main compatibility issue in such a case might be whether common elements - such as for menus, navigation, etc. - changed between previously delivered chapters. That is, maybe a right arrow for Save screen navigation was previously a .JPG but in Chapter 3 became a .WEBP (which otherwise looked the same.) If something like that happened, I suspect that combining all game chapters into one package would simply lead to referencing a consistent set of common images by easily searching out old filename references and replacing them with the latest names.
Otherwise, the Ren'Py documentation doesn't seem to indicate you can't combine different image formats in a single package, let alone a single screen.
End of DMD too sad to think about.
Geez, we just got Chapter 3 and already the end is in our minds again! Ahhhhhhh
hhhhhhhhhhhhhhhhhhhh ... *