Dear Florian,
The blade structural module in FAST v7 and in the ElastoDyn module of FAST v8 do not have chordwise CoG offsets from the pitch axis. However, there is still a mass component to the pitching moment when the blade deflects, as discussed briefly in the following forum topic: Blade Twist Deflection.
The new BeamDyn module of FAST v8 supports a much more sophisticated blade structural model, including full geometric nonlinearity supporting large deflection, with bending, torsion, shear, and extensional degrees of freedom (DOFs); anisotropic composite material couplings (using full 6x6 mass and stiffness matrices, including bend-twist coupling); and a reference axis that permits blades that are not straight (supporting built-in curve, sweep, and sectional offsets).
Best regards,