Why is this a cool thing?
Because, per the authors, the goal is to grow retinas that can be transplanted or to use programmed stem cells that can be injected into an eye to repair a vision deficiency.
What is the other takeaway from this lab-grown retina study?
They learned more about color vision deficiency. By watching the retina grow and develop over time, they were able to see the mechanisms on how color vision develops. They discovered that this development seems to be related to a release of thyroid hormones. The team plans to investigate this relationship further. (via here and here)