I would not hold my breath waiting for this to happen. I'd say this is one reason the Dot came out; so they didn't have to do this to Echo, even if they could; (assuming it has the hardware to do it). Why should Amazon do this if they can now sell Dots for that purpose? Also, why is the Dot a transmitting device only instead of both a TX and an RX device? (They could have done this if they had wanted to. (I have a tiny BT dual mode TX/RX device and is same size as a TX-only device.) So they can sell more Echos and new Taps is why.
I believe there is a method to their madness; Amazon is shrewd; not stupid.