The 2 things here I care about most: my XFWM theme (uses .xpm files) and Window Manager Tweaks (hide titles of windows when maximized)
Though I am still fine with X, and also stagnant on updates (due to various issues).
I understand your concern.
At this point, there are no plans to deprecate support for X11. So, if your config is working now with 4.20, it should still continue to work with Xfce 4.22. I can't say for sure how, of if, your concerns will be supported with xfwl4. I'd recommend trying xfwl4 when you are comfortable and file bugs against it if your current config doesn't work.
It's still to be determined if/how the next release of Xfce(4.22) will incorporate the work currently being done with xfwl4.
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