Cross-compiling is a need that almost no user ever has.
The only legit need on macOS was for a long time iOS only and now, the two supported CPU architectures. But that is covered by using XCode.
There would be now need for a Apple Homebrew to use or provide universal binaries.
Homebrew's design is for providing tools for the need of the single user of the system (it doesn't even work well in a multi-user environment) with the tools he needs on this system. Switching CPU architecture would be solved with reinstalling Homebrew on the new system (like it is now).
The only legit need on macOS was for a long time iOS only and now, the two supported CPU architectures. But that is covered by using XCode.
There would be now need for a Apple Homebrew to use or provide universal binaries.
Homebrew's design is for providing tools for the need of the single user of the system (it doesn't even work well in a multi-user environment) with the tools he needs on this system. Switching CPU architecture would be solved with reinstalling Homebrew on the new system (like it is now).