iFixit:

The issue is fairly simple: the current generation of MacBook Pro laptops (2016–present) uses flexible ribbon cables to connect the display to a display controller board beneath the Touch Bar. These cables wrap over the board, where they’re secured by a pair of spring-loaded covers—and they’re subjected to the stress of bending with every opening and closure of the laptop. Within a seemingly short time, those cables are starting to fatigue and tear. The backlight cable is generally the first to go, producing the infamous “stage light” symptoms, and eventually giving out entirely when the laptop is opened more than about 40°.

And:

Apple opted for thin, fragile flex cables as opposed to the beefier wire cables used in previous designs that could be routed through the hinge instead of wrapped around it, helping mitigate the stress of repeated openings and closings. But the bigger problem is that, in an apparent effort to make the display as thin as possible, Apple designed the cables as part of the display, so they cannot be replaced. This means that when (not if) those cables start to fail, the entire display unit needs to be replaced, as opposed to one or two little cables—effectively turning a $6 problem into a $600 disaster.

Take the article with a grain of salt. This isn’t necessarily doom for the MacBook Pro, or even that big a deal.

But, if you do experience “stage light” symptoms, this design issue is important to be aware of. If you do run into this problem, I would definitely go into your Apple Store discussion armed with a bookmark of this article.