The Expander has the USB ports so without it you won't be able to load new patches.
Once you have stored the patches you want, you could run without the Expander with no problem.
There is an additional micro USB port on the back of the module, we recommend that you DON'T USE IT! (sorry for shouty voice; the module may try to power over USB which this connection can't handle, and a small surface mount power switch will probably blow up and let the magic smoke out.)
And yes more Expander functions are coming. But you already get: line level /headphone input and output stereo jacks, and USB A and B ports for connecting to computer and MIDI gear.