Yes, to avoid various forks of the legacy GLES implementation having their own local patches, I think it makes sense to review and accept patches on this branch, as long as it doesn't become a significant burden. We do want people to switch to ANGLE + SwiftShader Vulkan (aka "SwANGLE") at their earliest convenience. We hope to make that solution a little easier to build once its integration into Chrome is complete.
Regarding the non-deterministic sampling, I believe we fixed that issue on the Vulkan side several months ago. It was caused by using vector registers with 16-bit components to store 8-bit color components in the upper part, but the lower 8-bit was left uninitialized. When used in filtering, the lower part affects rounding when we extract the upper part again. Anyway, in short, moving most of the code from src/Pipeline/SamplerCore.cpp to src/Shader/SamplerCore.cpp is likely to address it.