This is a really good idea, and long overdue.
There really is no traffic on Congress north of Sixth. Congress dead-ends into the Capitol at 11th, so the only traffic on Congress is whatever is coming from north/south of 7th to go over to I-35 on 11th. And that's really not much.
With no vehicle traffic and with very little in the way of office or residential north of 7th, there's little to keep retail/restaurants in business. The only things you have are a couple small restaurants and a coffee shop. It's really the only area in downtown that you have a bunch of empty storefronts.
Pedestrianizing roads is great for street-level retail. It is an absolute magnet for pedestrians. And pedestrians are more likely to go into street-level retail than car drivers. After seeing something they might want to visit, a car driver has to find a parking space, get out of the car, and walk over to the business. A pedestrian just has to walk in. For an example, just take a look around Madison Square Park after Broadway was pedestrianized. Or take a look at Akard & Jackson streets in Dallas. Or fuck--look at Speedway on campus and how much nicer that is than when most of us were students.
If you pedestrianize Congress north of Sixth, you'd turn a lot of those empty storefronts into some of the most desirable retail in the state.