They're going to need icon and font support for the retina, otherwise they'll need to scale everything which would work, but it won't look that good.
The TN panels are still pretty good, I believe the TN panels require less backlighting for the same brightness levels, helping with battery life. Response time is usually better with a TN as well. Just different trade offs.
The screens in the MBP are vastly better than most TN screens used in cheap notebooks but aren't as good as comparable IPS screens on the HPs, Dells, Sonys etc.