Oh my.... this is a really long thread...

GNOME Software Center can show/hide
any applications they want, they can even
just choose to hide all KDE/Qt apps just
for the sake of not liking them.

AppData and AppStream have to some
extend little to do with GNOME Software
Center on our land, most KDE users won't
be using it to install stuff, so what we can try to
control is Apper and Muon.

For the record Apper will be supporting
AppData and AppStream, but by default
I'll choose to do what Ubuntu Software Center
does which is hide packages that aren't
listed as applications, with a tip that the
search matched packages too.

This is what I believe to be the best option
since I don't like the idea of opening a terminal
to install devel libs even if the developer is
supposed to be a bit smarter...

Apper already supports AppStream but
it's clearly not in a nice fashion, as soon
as I port it to Qt5/QML it will be comparable
to a real Software Center.

That being said I think something to worry
is that we need to change something or not,
the sooner we spot a weak point the better
since changin specs we all know it's a mess!

Also if KDE people decide not to support
AppData and AppStream it is just sad as
Apper will end up listing only GNOME apps
as applications...

Best,

-- 
Daniel Nicoletti

KDE Developer - http://dantti.wordpress.com