According to a Dallas Morning News article about HOV lanes on US 75, the plans have changed for HOV lane implementation between I-635 and north Allen.
The HOV system would have been a single, counterflow HOV lane. Now it’s going to be like the HOV lanes on I-635: one dedicated HOV lane in each direction.
It’s good news if you don’t like speeding tickets: it eliminates the left shoulders, making it more difficult for cops to sit behind a radar gun.