Good point! Best optimized kernel as default. We don't have to support different types of hardware. There's only one n900, so yes to NEON and other such optimizations too.
You know, Arch means anus in German, nevertheless its base repo is a good starting point.
But before going into extras, GL-graphics etc., I'd like to cater for early options and alternatives to it like a busybox base, a plan-9 base and statically linked bases. The philosophers have some interesting thoughts about these http://sta.li/