Much of the Epilogue of Guns, Germs, and Steel is devoted to Diamond’s vision of and agenda for the study of history in the future. You can see this starting at the bottom of p. 408.
On p. 408, Diamond starts to lay out his vision of what history could be. He says that
The challenge now is to develop human history as a science, on a par with acknowledged historical sciences such as astronomy, geology, and evolutionary biology.
Diamond believes that historians have not been very scientific in their approach to studying history. He says that they need to move in that direction. After p. 408, Diamond leaves this idea, but he comes back to it and discusses it at length beginning on p. 420. On p. 426, for example, he says that historians need to look at natural experiments of history as he did with the example of the Maori and Moriori early in the book. This is his major vision for history.
As for an agenda, Diamond starts to lay that out on p. 409. He says that historians should go into more detail about the differences between the continents that Diamond talks about in this book. For example, where he compared the number of large-seeded grasses on each continent, they should expand by looking at the numbers of legumes. Next, he says that historians should look at
smaller geographic scales and shorter time scales than those of this book.
He wants them to try to determine things like why China was powerful up until a given time and then lost its lead to Western Europe. He did not explain this at length in his book and he wants other historians to try to work on this sort of question. On p. 417 he says that historians should look at the effects of culture. On p. 419 he says they should try to determine how much impact individual people have on history. These are the main aspects of his future agenda for the discipline of history.