It hasn't gone anywhere, really. The idea of having all modules from the same maker goes back to the beginnings of synthesizers, when you had to rely on full systems from a manufacturer. The difference now is that all of these different full systems can 'talk' to each other plainly, whereas before you had all sorts of different CV and gate/trig standards that weren't always compatible. Full systems give users the ability to use that older paradigm...but they work just like any other modular in that they speak the same CV/gate 'language' and, if you desired, you could pull one of the full system's modules and drop something of your own preference in. That's the point of modular.