To be clear here, we don't have a compositor yet. I've done a little work on it, but it won't be usable for at least a year, maybe (probably) longer. 4.20 will let you run some of our components on another compositor. We mostly test with Wayfire and Labwc, as our compositor will also be using wlroots.
Btw I love xfce. Find it to be the perfect balance between features, stability and performance!!!