What is the team's overall direction for that area of code? Is it as simple as "it just has to work"? Are there things about how it works that aren't expressed in code but have to be preserved? Or do you have plans for how you're intending to change it in the future?
It is complicated and always evolving. The ntdll tests certainly capture a lot of requirements, but not everything. What's making matters more complicated is that DRM and anti-cheat systems hook into ever-lower levels of ntdll, and we have to do our best to replicate how things work on Windows.
What is it that you are trying to do in the loader code?