I ended up joining the ANT developer network, which is free, when I was thinking about tinkering. Is not very tinker friendly.
To be ANT+ (with plus sign) you need to obey the rules of specific profiles. I didn't see any that would allow them to transmit the more complicated data Runscribe collects. They could do Running Speed & cadence though.
I haven't got one, but the newer Garmin devices have something called? Connect IQ, which would let them use their own ANT (no plus sign) to transmit those metrics. The problem is that it would be Garmin only & only newer Garmin devices. For instance the 910xt is already too old.
Live cadence would be awesome though. As would cycling cadence, which would probably be easier to implement. The Wahoo cadence sensor can be shoe mounted, so it is definitely possible.
Transmitting using bluetooth might be easier than ANT+, as it already uses BT, and works with more phones, but would not work with garmins.
I join you in hoping something happens.