They are completely different products,in musical, conceptual, functional and software terms. I cannot see how they could be bolted together and still keep all the functionality.
PS The ST3 Custom Shop (the free one) will load instrument libraries, such as Syntronik. But Syntronik is sample-based with a fixed set of controls and "MODO BASS is the first technology of its kind that models the entire process of playing bass. Every component that contributes to the unique tonal properties of a bass player playing an instrument has been modeled,..."
With all due respect, DAW's do this all the time, they take many different types of programs from many different vendors and allow them to be integrated into one work environment.
So from a programming POV I don't see an impossible or unacceptable task in integrating MODO BASS, Syntronik, or any other computer software made by IKM into their proprietary ST3. Also consider that ST3 already has components from every type of software products IKM already has i.e; effects, amps, tracks, etc.
I would really like to hear a reply from IKM on this.