Sidney posted a detailed write-up a few days ago as to why developing an add-on by modifying our shaders is not a good idea. The short version is that, like art controls, the shaders are an internal part of X-Plane that we don’t lock up so you can see them and muck around with them. But there is no stability, documentation, or any attempt to make them useful the way the plugin system is.
This confused a number of commenters. Do we want you to use them or not?
To resolve the mixed messages, Sidney created this fantastic flow-chart.
Hopefully that clarifies where the line in the sand is between “I was poking around” and “I made a serious add-on”. Pretty much everything here goes for the shaders as well as the art controls, only more so.