3D printing the fin assembly has limitations related to size and strength. The chosen 3D print material and 3D printing technology will dictate the strength and size limitations.

FDM (Fused Deposition Modeling) is the most common / hobby 3D printing technology

FDM printing material has come a long way and there are advanced materials available that includes carbon or glass reinforcement. 

However these materials do not allow for the strength and stiffness required to successfully achieve MACH flights.

Advanced resin materials such as Form Labs ‘Rigid 4000’ or ‘Tough 1500’ are strong materials and a printer such as the From 4 or Form 4 L can produce tollerances in the 0.001″ range.

Unclear as to how stiff the material would be as it relates to fin flutter.

Selective Laser Melting (SLM) or Direct Metal Laser Sintering (DMLS) 3D Printing will allow printing using aluminum power or other exotic metals such as titanium and will result an extremely strong and light component. 

However the cost of this for the hobbyist is prohibitive.