I believe that Dallas can support these developments, and a lot of well-heeled players are rushing to be near the front of the line. With the density that Dallas will need as its population grows, we likely will have enough people to fill these places.
I think that 'new to Dallas' residents will fill these spaces along with upwardly mobile college grads that decide that they want to be in the city and not the suburbs. I do think there will be an "arms race" to see who can best attract residents. Some will do well and some will struggle. But when you look at it, there can be a ton of coffee places, dry cleaners, etc because the client base lives right above or in the same complex as the business.
In cities like New York and Philadelphia, it's a way of life. Every pizza store and neighborhood grocery store has people that live above in condos or apartments.
When you consider the projected growth of Dallas' population, you can see that most of these projects will be a success. The key will be to ramp up infrastructure to meet the needs of the influx of residents.
However, one interesting thing is that there are now no first-run large scale movie theaters south of Northpark Center in Dallas (I'm excluding places like the Magnolia and the Angelika which lean towards lower-profile movies). There seems to be an opportunity for someone to build a large movie center. Surely AMC Northpark can't serve everyone.