What I like about the plot of Animal Farm is that it can apply to any society at almost any time. The principles in the book clearly demonstrate human nature.
- When one group obtains too much power, even if it is a small group, if it's goal are evil or even just selfish, it can destroy a much broader group of people.
- When people stop thinking about holding leaders accountable or keeping them in check, they become victims of their own circumstance.
- When there is a revolution among a people, it almost always takes out a leader and creates a void of power. That void turns into a vacuum. Something must fill it, and that often is a new person, who because of human nature has selfish tendencies and most likely inexperience.
I wouldn't add anything to the book because it already has very clear connections to the aftermath of the Russian Revolution. No more conclusions need to be done. That was history, and this is now. These principles need to be guarded against today.
I think that it depends on whom Orwell thought of as his audience. For example, at the time the book was published, Orwell obviously didn't care if he offended England's "Allies" or other readers--he simply wanted to satirize the many problems of the Soviet Union's totalitarian regime and to demonstrate how a "people's" revolution can go awry. During Orwell's brief lifetime, I don't think that he needed to provide any further events because his readers should have already been familiar with the failure of the Bolshevik Revolution in Russia to bring about a prosperous, free state.
That being said, if Orwell intended for Animal Farm to be timeless, if he had added more events before the book's opening, readers probably would not need as much background knowledge to truly appreciate the book. As far as adding more events to the conclusion of the book, that might be problematic because Orwell did not live long enough to see the downfall of the Soviet Union. Similarly, in Animal Farm and 1984, Orwell seeks to illustrate the hopelessness of the common man who lives in a totalitarian state. Thus, the animals plod on at the end of the book while the pigs gain more power, and nothing improves.