401 - 407 is being widened from 7 lanes (4 northbound, 3 southbound) to 8 + 2 HOV, 407 to Queen Street is being widened from 6 lanes to 8 + 2 HOV. overall throughput onto the 401 is only going to experience a small increase. Expect the 407 to start getting busier though.
Its one of a couple of big HOV additions over the next few years. the 404 is going to get HOVs up to Stouffville road and the 427 is going to go from 5 lanes (3 southbound, 2 northbound) to 6 + 2 HOV from the 409 to the 407. Then of course there is the 401 Express collectors expansion which includes HOVs and from my understanding is currently funded to Trafalgar road.
I suspect the 400 will be getting some HOVs added in the 2014 southern highways program from Major Mackenzie to King road as well.