Syncthing Tray is a Qt-based tray application to integrate Syncthing with Dolphin/Plasma. It is currently available in the Case_Of and jm-overlay overlays but it would be great to have it in the official tree complementing net-p2p/syncthing.
I would say your best bet to have it included is to proxy-maintain it yourself. Between the fact that I run Syncthing as a systemd service and simply use the Web UI on the rare occasions I need to change anything, and that I do not use Plasma (yes, I _have_ read that this can be used without it - but it seems whoever ends up maintaining this should be able to runtime-test Plasmon functionality), I shall not volunteer to maintain syncthingtray myself.