Idea: Runtimes appended to AppImages

Just some food for thought for future consideration. Not something to be rushed.
I shared this idea on IRC today:

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it seems that some people like the idea of having runtimes, so that the AppImage + the runtime = no dependencies on the system other than the kernel
so far, i was heavily opposed to it. but here is some food for thought:
what if we _appended_ the required runtime to each AppImage
another squashfs
which gets downloaded if you regularly download
which can also be left away (e.g., HTTP Range Request) if you already have/dont't want it
the default is that you get it, but you can opt out
something like that
just an idea for now
(might become AppImage image type 3 one day?)
Example:
https://github.com/Hackerl/Wine_Appimage/releases
the AppImages there all need Wine-x86_64.AppImage to run
they need nothing else from the system
they have their own glibc and ld-linux
i imagine that we could have one KDG, GNOME, KDE, WINE,... "RuntimeImage" per year or so
that people could depend on by appending it
who downloads it with a browser downloads the whole thing, who downloads it with something like AppImageUpdate would only get what they need
but as i said, just a vague idea at this point
(just had the idea after having argued with distro people how bad AppImage is because it lacks runtimes yesterday, and having seen what our Chinese friends do with AppImage and WINE today)
```