It is not a sin to offer "money for features", from a programmers perspective.
Most important is the way you intend OpenSource.
OpenSource is not meaning "free as air", but usually "free as a beer".
In the sense that you could offer a beer but you have to pay someone to make it (if you are not brewing it youself, but even in this case you have to pay money to make the beer).
You invest some of your valuable time, maybe subtracted to family or other things, to make something, "pro bono" could be another definition.
Sadly many people came here, to find an easy substitution for "payed software", in this case asking "money for feature" will be the right way.
As FreeCAD is made as is if you want a different behaviour you could find some ways:
1) code it yourself, and as you want it for free, make the code free for everyone
2) find some programmers that have same interest and his available to code it for free and integrate in FreeCAD codebase
3) fork FreeCAD and make your own version
4) pay a programmer and use the code only for yourself.
As I made some "work" using FreeCAD I have done some work following the 4th point, and my customers are usually satisfied.
But I even made some work for the Wiki (not very much, but there is a different approach to Part Design tutorial in progress)
And I have done some articles trying to explain some obscure things (not very difficult, but sometimes not so obvious).
But even when I work "for free", maybe writing code to help users on the forum (sometimes it happen that I write something useful) I use my time and when someone satisfied by my help had send me some money (sadly not very often
) I have been very pleased and grateful as being unemployed it will help to feed family.
And I suspect that seeing how thing are going, I think not be alone.
But many people came here "pretending" to have fulfilled their needs "without paying anything" even in term of efforts to explain and learn how things are working. Latest times it happens very often, so I could understand the "pay for feature" mechanics, even if this lead to some "reserved" work not shared between the majority of users.
In the meantime, Mario (hoping having guessed your name from your nickname
@mario52) thanks for your hard work creating Macros and helping user of FreeCAD. As I see that even receiving thanks and appreciation for your work is not so usual these times.
Kind Regards
Carlo D.