@Heiko Pardon me for asking a very elementary questions. What purpose does the motif serve?
I'm guessing that it has traditionally been used as a way to differentiate one release from another in a decorative way. If so, how open would the organization be to dropping it altogether and focusing instead on cleanliness? Here is why I think you should consider doing so:
Any symbolic value is nominal. It is difficult to identify symbols for abstract ideas like freedom, transparency, openness, etc. that transcend cultural boundaries. If this is the objective of the motif, it will almost certainly be lost in interpretation.
It detracts from the brand. A geometric motif that changes from release to release is at best to be forgotten with the next release. At worst it is distracting from the most important shape to the brand, the document icon. Why risk diluting your brand for something so transient?
It's out of fashion. Imagery that serves a clear purpose is never out of fashion, but elements that primarily serve some decorative purpose fell out of favor several years ago. The brand will feel more contemporary without what amounts to a wallpaper.
I know this isn't why you posted this project, and may not be what you want to hear. But I think the LibreOffice brand would benefit most from tasteful subraction, and subtle refinement of its core brand assets. I'd be willing to contribute some visuals to illustrate what I mean by that, but I'd first like to know better why as a new contributor my opinion is wrong. Please tell me more.