I have a ticket open on this issue for reference - Income is not being included within the Spending Plan module even though I am told that is not by design.
Sections like Bills that are assigned to Business categories also do not appear alongside Personal categories (at least on my instance they do.)
Note: At first the expense categories seemed to appear. This it seems is because when I first set up QBP I moved/reassigned certain categories away from Personal parent categories to be sub-categories of a parent Business category. This saved a lot of time setting up Business and the P&L report picked them up.
BUT . . . when reassigning the Recurring Income or Expense reminder (edit the series) to the Business category, the reminders disappear from the Spending Plan.