currently, xfce always keeps the panel above all windows. it's possible to suppress this with some window manager hacks, but then the panel always stays below the windows, which is also not desired - it should raise itself when it's hovered or it demands attention. kde5 implements this in cooperation with the window manager via the custom _KDE_NET_WM_SCREEN_EDGE_SHOW property. see https://git.reviewboard.kde.org/r/124272/diff/ and https://community.kde.org/KWin/Screen_Edges for some context.
To be honest this sounds a bit like "intelligent hiding". And even if there were differences, I don't think we desperately need yet another auto-hide mode (when the current ones still have some quirks).