That tension between freedom and technical viability is such a real design challenge. Grid-based is safe but can feel rigid — you lose those satisfying organic curves. Marble World's approach is interesting because it finds that middle ground where pieces still connect predictably but the layouts can feel more natural.
One thing that might help: a hybrid where the connection points are socket-based (specific attach points on each piece) but the pieces themselves can be placed freely in space. That way you get the precision of snapping at joints without forcing everything onto a grid. Kind of like LEGO Technic vs regular LEGO — more angles, same satisfying click.
Whatever you land on, the fact that you're thinking about it this carefully before building it is a good sign. Looking forward to seeing how it evolves! 🏎️