Despite Clavell’s other works having minor ties to Shogun (The Asian Saga), the novel concludes the story of Blackthorne and his relationships with the main players.
The end of the novel and the series conclude that tale and that’s how it needs to stay.
This is because the series was based on the novel of the same name by the late James Clavell, who didn’t write a sequel.
The ending was perfect and aligned with how the novel and its story ended – what more needs to be added?