I think optimal Trajectory Planning is a more complex task than implied here. High speed motion through 3D paths can involve the analysis of hundreds of GCode blocks/segments, each involving multiple axes, and where each axis has multiple constraints to consider. Additionally there can be path filtering, smoothing, blending, and kinematic requirements. I'm not aware of any controller that handles this problem well internally.My only question is why would you do the trajectory planning outside of the Galil controller? Trajectory planning is what it is designed to do, and they do it very well. Just tell it where to go, give it speed and acceleration, and let it do its thing.
Systems based on Mach3 (including our own plugin) rely on Mach3's Trajectory Planner which sometimes has issues as I believe relatively few segments are being collectively considered. Settings may either result in slow jerky motions, or fast motion, that may deviate from the specified path by an unconstrained amount.
For these reasons we run our GCode Interpreter, Trajectory Planner, and Kinematics on the PC in order to take advantage of the PC's vast resources. As long as a PC is available whether the GCode file is submitted to a PC Library, or directly to the Controller, is normally transparent to the User.
I think you will find Controllers that accept GCode directly, and do Trajectory Planning internally, to be very limited.