He's a one-man army of a one-year old software, so it makes sense that he would focus on core features that are most relevant to his existing customers and capable of attracting new ones. If this was important to you or someone else who would sign up for a Symbolica license, I'm sure he would improve on this. A streamlined C++ API is comparatively easier to achieve than beating state-of-the-art efficiency on key CAS algorithms...

We should encourage this original approach of licensed source available software, otherwise you end up with either black-boxy Mathematica-like software of xzlib disasters and nothing in between.