Hi @AlexisJazz thanks for filing this! I've moved the task for our team to discuss.
Thank you! Where will this discussion take place, can I follow it?
As I'm aiming to get my userscript released soon, I've implemented a kind of echo-emulation into it. Simply put it stores notifications in a userjs- preference and tacks them onto .mw-echo-ui-notificationsListWidget. It has endless limitations and will probably not be much fun to maintain, but I needed the functionality. I'm looking forward to being able to echo oneself so I can dump that ~18K of rubbish code from my script.