Yeah, that's true, but the good thing about subtags is that they can be done without any changes to anything, so just decide on some of them, use them, and they're active :)
Of course, I really do want to changes to the tag system, either from the blockchain directly or from the Steemit UI. It's not working very nicely at the moment..
I'm not sure either case would require changes to the blockchain itself. I'm going to do a garbage post to see if machine tagging works on the blockchain or if it will break.
It seems to break. lol. This is okay though. I could just merge the ideas. #tag--subtag---value. This could still provide something easy for a script to parse. and its instantly usable as you say.