app-vim/dbext-5.20 works ok on amd64 architecture. By the way, this plugin doesn't contain any arcitecture-specific code, so it is seems to be reasonable to enable it on all architectures.
6.20 is ~amd64 keyworded already. Keywords: dbext-6.20: ~alpha ~amd64 ~ia64 ~mips ~ppc ~sparc ~x86