1. Go “complete” CSD/HeaderBar (i.e. redesign every application to truly benefit from introducing a HeaderBar)
2. Full CSD, not full HeaderBar (use CSD only as window decoration for apps, replace XfceTitledDialog with a HeaderBar)
3. Use CSD only for XfceTitledDialog (replace XfceTitledDialog with a HeaderBar, applications remain decorated by Xfwm4)
4. Stay where we are (well, literally change nothing about our decorations or XfceTitledDialog)

This is the most effort of all three scenarios and would imply redesigning all applications, notably Thunar, Parole, Taskmanager.

Benefit:

• We go for a complete and hopefully consistent transition

This means

• replacing XfceTitledDialog with a HeaderBar containing “[icon] [title|subtitle] [window controls]”
• re-designing those apps that seem like low-hanging fruit (Taskmanager

Advantages of current XfceTitledHeader:

• Unique design element that only Xfce has (probably the only one)
• Big icons and big/bold text make the purpose of the dialog very obvious

Downsides of current XfceTitledHeader:

• Uses a lot of vertical space
• Duplicates window title
• Means apps or plugins always have to rely/depend on libxfce4ui to get an “Xfce Settings Dialog”
• Pesky/laborious way of creating window decorations / xfwm4 themes

Advantages of Headerbars:

• Less vertical space used (at least in Settings Dialogs)
• No more window title duplication
• No need for custom widget - every app developer can set it up him/herself
• XfceTitledDialog code could be reduced to a fraction and after a transition period dropped completely
• Other action buttons can in theory also be packed into the Headerbar
• Users cannot match titlebar style and Gtk style independently (so it will always look consistent)
• Enables dark mode (apps which request the dark Gtk theme variant will now get consistent decoration)

Downsides of Headerbars:

• Users cannot customize the buttons in the titlebars anymore (only the window controls layout)
• Users cannot add special Xfwm4 buttons anymore (menu, stick and shade - although menu is always there on right-click)
• Risk of inconsistency if we don't write down good guidelines how headerbars/CSD should look in Xfce (example of possible inconsistency: app icons or not, window title or not)
• Users cannot match titlebar style and Gtk+ style independently (so if they don't like the look, they have to search for another theme)

The screenshots always show the current style first, then the new style. The theme is Greybird, although some shots also contain Adwaita (in addition).

Relevant for Scenarios 1, 2 and 3.

Relevant for Scenarios 1, 2 and 3.

Relevant for Scenarios 1 and 2.

Relevant for Scenarios 1, 2 and 3.

Relevant for Scenario 2.