I have seen that ebuilds are bloated with information from different architectures. If a different tree for architectures is made it will help in following ways: 1: making the ebuilds clean/less-bloated 2: contributors who do not have knowledge of other arch, can easily contribute 3: testing would be easy 4: maintaining ebuilds would be easier 5: the problem of (stable for x86 but unstable for ppc(aor any other arch) would be solved Reproducible: Always Steps to Reproduce: 1. 2. 3.
See discussions on -dev mailing list as to why it is handled as it is.