I'm using newest KDE Neon 5.9.4. My Spectacle version is 16.12.3-0neon+16.04+build31. kipi-plugins - 4:5.4.0-0neon+16.04+build14. gwenview - 4:16.12.3-0neon+16.04+build26. I installed kipi-plugins from APT. In gwenview their are visible and I can export image to many online services. In Spectacle this options aren't visible in "Export image". It was working as supposed in latest Manjaro KDE. I was able to use kipi-plugins in Spectacle.
Works for me in Spectacle 17.12 in Plasma 5.11.5 with kipi-plugins installed. Can you reproduce with the more recent versions?
If you can provide the information requested in comment #1, please add it.
In the newest version everything works fine. Thanks!