Definitely voting for "arch.list". In addition to its current use by portage.{py,5} (as mentioned by Mike), its name is more descriptive. I have been wondering about the naming of the KEYWORDS variable(s). Usually the term "keywords" refers to search-fodder, categories, and other generic flags. Any Portage gurus remember how it ended up being specific to architecture flags? IMHO, "KEYWORDS" in the ebuilds should be renamed "ARCH_ALLOW" and "ACCEPT_KEYWORDS" in make.conf should be renamed "ARCH_ACCEPT", just for consistency with their usage. But that's probably a discussion for another thread.
-- 
Batou: Hey, Major... You ever hear of "human rights"?
Kusanagi: I understand the concept, but I've never seen it in action.
  --Ghost in the Shell