If you want any of this, why don't you found a Verein and have open source activities as the purpose?
All in all I an very much against this. Mostly because I think Ehrenämter, as they exist now, are pretty stupid and pointless and because I strongly believe the state should not get involved with this at all.
The petitioners seem to be blissfully unaware how civil service is recognized in Germany. Or they are all too much aware and want to undermine transparency requirements by asking for special treatment for open source developers. The charity principle requires to assume the former.
What I wanted to express is that it is "just" various forms of volunteer work, which ranges between some occasional organizational work in a Verein to doing hard physical labor at 3 in the night. What the petition argues is that open source developers "deserve" the title of "Ehrenamt", which really is what I disliked about the whole thing. Because effectively it is just a designation, nobody does their volunteering for that title or any of the benefits it gives you.
The demands of the petition would be solved by just founding a Verein (which is exactly the structure you want to organize volunteer activity), but as you said, if you wanted to interpret the petition as negatively as possible, the petition wants to avoid having a Verein, which enforces a certain degree of openness and transparency about finances.