My personal pain points are bluetooth support and gamepad support being a bit of a mess.
Next big stepping stone for me is a Windows VM + http://looking-glass.io , which side-steps the graphics card driver question and doesn't require two monitors, though I don't know how hard that is to setup on FreeBSD.
Using just jails on my servers, no idea about docker.
FreeBSD has its own mechanism for that which is jails (and which predates docker!). If you're not using docker containers you pull from docker hub, I would recommend to use jails.
One thing I like is that the team maintaining the desktop apps is very responsive. Usually new KDE versions are pushed to latest within a day or so.
I can vouch for the complete opposite. I use sway, an i3 like Wayland compositor (compositor = window manager in the confusing wayland lingo), and its completely problem free, only changing kern.evdev.rcpt_mask to get input working and specifying a sway socket file thingy is needed. (Something I am confused as to why package maintainers don't set by default) Maybe the wayland mode of other Window Managers is broken, which can have both X11 and Wayland modes.
I use KDE by the way, I know of sway but never used it.