Having a smaller kernel would certiantly make it faster, but how would that make it more "secure" and in what way?
Not to mention you would have to have a much smaller library of call commands to mantain the kernel's micro status; thus reducing usability and compadability by alot. Which I guess would make it more "secure", but that's like saying you're secure against being robbed because you can't leave the house.
Why not just use base Unix if we are going this dinosaur? Why even have a GUI? We can make it even "faster" without one.