Would be great if Siri worked locally on the Mac to process dictation.
Cool dictation will be taken up a notch.
If you press Fn twice (Fn Fn), you'll enter dictation mode.
Your Mac (not iOS) should offer to download speech recognition locally to your Mac. It's over 500MB so it's not small, but it is quite good, I'm impressed.
So, if you're talking actual dictation (and I know you weren't macduke), yes, it can be done locally.
It's a heavyweight package so it's unclear if Siri could be made to work the same way. I know I'd take that option.