I would add a little to Victoria C.'s excellent answer. Let's look at it this way: a relative clause is almost always an adjective clause, as you say, modifying a noun antecedent. Now, almost any adjective can be used as a noun ("The good die young," "All are in agreement on this."). When a relative clause is used as a subject, it lacks an antecedent and then becomes an indefinite relative clause, in which the suffix -ever is attached to the relative pronoun or adverb.
You could, I suppose, write "Whenever it is good for us to meet has not been decided," but Victoria has a better suggestion. As to your second example, I would offer "Whoever is qualified for the job will be appointed soon."
