I'd say, and let be clear that I know and accept this to be a relatively arbitrary distinction on my part, that for an input to be "primary" it needs to be able to stand alone (touchscreen input, keyboard and mouse, etc). That's not to say that it must stand alone, but that when all other options are off the table, that would be your preferred method for text/data entry.

That's a troublesome definition though at least in part for reasons you've brought up or alluded to, which is that a multimodal approach is pretty clearly going to dominate. That said, speech recognition at least stands to replace the keyboard for say, the author of a book or article, if it's good enough.