It’s great to see some of the questions about shade variants, and that’s a complex topic!
I will link to a more complete answer I added in one of the threads here , but also let me take opportunity to call out some of the parts on that answer to your questions here.
There are currently discussions about exposing API that could allow users to find the balance between runtime cost vs memory/build time cost, by f.ex turn keywords into dynamic branch.
Several things happening. Shader Prefiltering is on PR review stage for 2023 and that brings massive improvements in shader stripping time. There is some work that recently landed to evict shaders from memory and improve shader memory footprint. Every release in URP we do a pass to find potential stripping improvements we might have missed, f.ex here.
We have added more documentation on shader stripping [1][2][3][4]. We currently have documentation in progress to document shader keyword in URP.