It sounds like your definition of "viable" differs from mine then.
It's certainly not a drop in replacement and certainly not right for everyone but one often hears "we couldn't use $x" when in fact what is meant is there is no impetus to use a replacement and that the users don't want to adapt entrenched behaviours.
That's fine but is quite different as an objection to "the software can't do what we need".
that's fair - Calc can do everything you need, so the objection is more clearly stated as it not being compatible with excel. You can't share files with excel users (like you can with Word and AbiWord or Writer).