Thank you geert for the elaborated answer.
I agree with prototyping with available materials to see the stress concentrators, which will help me in refining my design. I have already ordered the nylon filament, so even if it didn't work, I am sure it will be useful for other projects.
To answer your questions, the 3D Printed nylon piece is only used in a part of the wing rib (the flexing points) and not the whole rib frame. The rest of the rib will be mostly made out of wood (since the project targets miniature UAVs that dont need very strong wing). The rib will be covered with elastomeric skin (similar to Latex material), which is smooth and can stretch as the rib profile changes. The efficiency of the flexible rib wing is part of the investigation, but according to AFTI/F-111 mission adaptive flight wing program, it can increase range by 20-30% of a plane. It all comes down to how much weight the system adds, and if that additional weight will be compensated by performance increase. So it really depends on the design/materials the flexible wing consists of.