It's possible to have kwin automatically hide the decoration for maximized windows by setting:: [Windows] BorderlessMaximizedWindows=true in ~/.kde4/share/config/kwinrc. However, this option has no corresponding checkbox in system settings. It should have one, probably in Window behavior -> Moving. Reproducible: Always
It's Martin's choice but afair this was supposed to be used with the netbook shell only. Just FTR: there should be absolutely NO reason that systemsettings (at least the kwin kcms) ever kill this setting (should be altered only when you switch between netbook and desktop shell - out of personal experience: never do that, lead to giant mess up here because it ran around and altered random settings and didn't correctly fix them back, but that's quite some time ago)
I was actually thinking about removing the current implementation for the borderless maximize and replace it by a KWin script. Pretty simple: if (client.maximized) { client.noBorder = true; } else { client.noBorder = false; } plus of course some wrapping around for the case that the window should really not have a window decoration. That would automatically come with an option to enable it - as it would be in the scripts module. But for the current implementation I would not want to expose an option.
As a user, I don't know which implementation is better. However, if the implementation as a script comes with an option, then I support that :-) Of course, I have no idea if the change as a script is a good or bad idea from an implementation point of view, you should decide that.
*** Bug 330797 has been marked as a duplicate of this bug. ***
Unfortunately, either with the BorderlessMaximizedWindows setting or this KWin script <https://api.kde-look.org/p/1112547>, it doesn’t work on Wayland (both works on X.org). Is it not implemented yet or should I open a new bug report?
Borderless maximized windows will be supported on Wayland starting in Plasma 5.9. I recently added support for it.
*** Bug 383833 has been marked as a duplicate of this bug. ***
Regardless of how borderless windows are implemented, I don't think that it makes sense to expose this in system settings because it's mostly useful for unity setups, which requires integration from either the window decoration or the desktop shell. Arguably, if such an option is needed at all, it should live where window controls will be displayed, e.g. a panel.
*** Bug 451348 has been marked as a duplicate of this bug. ***