Jantje:
Anyways arduino:arduino is not supported by the plugin see this github issue arduino:arduino in boards.txt is not supported (for upload) · Issue #158 · Sloeber/arduino-eclipse-plugin · GitHubFor something else and with the change for the boardsmanager I considered to implement it but it turned out that even with the changes for the boards manager, it is not that easy. So I stopped searched for an easier way found it and deleted the code.
Ah, thanks for point to issue #158.
Hmm, too bad that you have given up on it, because it makes the plugin unusable for me 
Well, OK, I can find a work-around for myself. But it will be a hard to explain work-around for other SODAQ users. And Sparkfun, and Adafruit, etc.
But hey, this is open source. If you want something you can do it yourself. 
The only(!) problem is to find time.