I’m a bit worried to hear that the application dashboard is likely to be removed in Plasma 6, since that’s the one I have been relying on for the past years.
My setup is a desktop machine with a 24" 16:10 monitor (1920x1200 px) with no touch support, and application dashboard is really working great for me!
Thus I hope any replacement like the mentioned new fullscreen Kickoff prototype could also be used properly with mouse + keyboard input (without touch support)…
My biggest gripe with application dashboard (and why I could never use it) is the misuse of space and no way to configure it.
So, the input that I can offer is to have some configuration option to choose the size of the grid, and maybe the ability to choose which view is default at launch (e.g., favorites or all-apps).
Also, are you planning it’s fullscreen view to be like the overview-effect/present-windows, or just as it is in the prototype you shared? FWIW, I think it would be cool to keep it consistent, following the UI of the overview effect.
Setting the default view at launch makes sense. Size/number of grids should also be possible.
I am not sure making it look like Overview is even possible because of the extra user avatar and power buttons, and using the desktop background will require it becoming a kwin plugin, but blur background should be possible with KWindowEffects::enableBlurBehind.
I think that using the blur background property while keeping the UI elements (e.g., search bar) similar in size and style to the overview effect could work, and in my opinion, would definitely make a nice addition to the “official” launchers.