We already know from GNOME devs' work they are ok with intentionally creating obstacles for the user - intentionally making titlebars huge to justify CSD, intentionally making the tray to an unobvious place before deprecating it, deprecating the tray when lots of software uses it.
But not only do they not have any respect for their users. Here's a GNOME dev's reply to a thread on tray icons in Transmission.
I guess you have to decide if you are a GNOME app, an Ubuntu app, or an XFCE app unfortunately. I'm sorry that this is the case but it wasn't GNOME's fault that Ubuntu has started this fork. And I have no idea what XFCE is or does sorry. It is my hope that you are a GNOME app. Yes this kind of fragmentation is unfortunate. I'm not happy about it either. Anyway, I just wanted to give you a heads up. Wish you the best.
You cannot realistically "not know what xfce is or does" as a desktop FOSS developer. Pretending to not know a project to devalue their effort is none other than an insult.
Saying that starting Unity development is Ubuntu's fault warrants no comment to be seen for what it is.
I'd like to ask desktop-oriented FOSS projects to consider if this is the sort of project they want to support by giving special care to be compatible with. Accounting for tray icons not being there is accounting for gnome specifically - everything else has them, even bare WMs like IceWM. Maybe, it's better to leave the gnome user experience be what its developers intended it to be starting from the 3rd release - broken.