That’s exactly what it is in dwm (except that dwm defaults to using alt as the MOD(ifier) instead of super, but changing that takes only a one line patch). And you can also just use MOD-leftmouse-drag to move a window or MOD-rightmousedrag to resize (either of which change the window to floating mode if it isn’t there already), or use MOD-middlemouseclick to toggle its floating state.