We wouldn't. Just because something can be done doesn't mean we have to implement it. How would a user actually know what exactly is the point 3*A.x + 5*B.y + 7*C.z in space? And if the user doesn't know, how would he use it then?

Adding functionality without proper use cases just bloats the software and dilutes the actual capacity of the software.  If you can let me know of use cases for this, I'll add this functionality.