Absolutely, it's simply a difficult task.. they've been tackling it for decades and it's still nowhere near usable, assuming you would ever want to use a Windows-like OS.
@J65nko, IMHO, Plan 9 went in the wrong direction.. it's so unlike Unix that it simply seems unappealing on so many levels.
Take this
comparison of Plan 9 and Unix, it just makes me feel dirty.