I suppose the software is upgradable, though I've never heard of any option to do so. Without all the capabilities of the Legacy base, I suspect that isn't really much of a factor.
The BASE1L is basically a new replacement for the old TMCC BASE. I like the CAB1L as I can connect to the Legacy system with a smaller and more robust remote that is not so easily damaged. For common running sessions, I don't really need the features of the CAB2, so the smaller remote is just "handy".