Here is another future rule of English grammar (we have already given other speculative rules of future English grammar here and here). In a sentence with a predicate noun, the verb agrees in number with the predicate noun, not with the subject.
This phenomenon is already so common that Dr. Boli may be mistaken in calling it a future rule. We may be forced to admit that it is a current rule of English grammar.
Two examples taken from the unwashed Internet:
I agree that the biggest threat to WordPress and its reputation are the plugins and themes built for it.
The main object of the Nazi offensive in the summer of 1942 were the oil fields of Baku.
When Dr. Boli was learning English grammar, the rule was simple: the verb agreed in number with the subject. Thus he would have written threat is, not threat are, or object was, not object were. In current writing, however, it is so common for the verb to take its number from the predicate noun that Dr. Boli feels a little old-fashioned.
It seems a pity that this rule should become the standard in English. “Verbs agree with their subjects” is a very simple rule. “The verb agrees with its subject unless there is a predicate noun of a different number, in which case it agrees with the predicate noun”—that is the sort of rule that gives students of languages nightmares. But Dr. Boli is not authorized to prevent these changes in the English language. He can only observe them and hope that they do not prevent him from communicating entirely during his lifetime.