I wouldn't be surprised if they do add some more functionality once they start getting some usage data, like how many times people actually use Siri on them. I'm taking a wait and see approach with Siri. I stopped using Siri altogether on my watch because of the crazy lag.I ordered a pair and waiting for it on 20th of December.
In the meantime, I could see and hope that in the future they will allow configuration of tapping.
Foe example:
Tap on left headset 2 times - goes to next song, 3 times to previous.
Tap on left/right headset once - get SIRI
Tap on right 2 times volume down, 3 times - volume up.
I wish for something like this.
I like your idea of taps to next/prev a song. I think that would be very useful to a lot of people. You're more likely to use that than Siri I imagine.