The robustness principle was fine for xembed. This isn't xembed. Xembed could -not- exist going forward, it wouldn't even -usable- on future systems considering the icons for xembed are hardcoded to be 22x22 pixels. 22x22 pixels looks like trash on my 1080p monitor, I don't want to think about what it would look like on a 4K monitor in the future. Better to just rip the bandaid off now when 4K is still gaining traction so that by the time it comes around we are hiDPI ready across the board. For KDE specifically trying to do an Xembed systray on a Wayland desktop via XWayland is, by Martin Graesslin's own words, "not the most trivial task."
I get that annoyance and inconvenience of your app breaking on Gnome 3 and KDE 4 systems, I have a few that broke too. But I was also there 4 years ago when Ubuntu and Gnome said "We're bin'ing Xembed at some point in the future. Move to Status Notifiers or AppIndicators or be left behind. Pidgin, Audacious, DavMail, etc all had plenty of warning it was coming.