What are the effects of Data Design & Modeling guidance from this webinar on Report design?
Decomposing the Loan Application case type from a large number of top-level properties to a smaller set of embedded "single page" properties (each of which becomes home to the properties from the top-level) has no impact on Report Definition design. If a property retains a one-to-one relationship with the Loan Application (for example, when .TotalExpenses became .FinancialPosition.TotalExpenses), this is just as easily selectable from a Report Definition on Loan Application.
The consequences for one-to-many data within the Case Type are unchanged. Declare Index rules and tables are maintained by Pega for any properties optimized within Page Lists, and Report Definitions natively traverse these.
When externalizing any Page List data to concrete instances (in Pega) of distinct Data classes, which your application accesses via auto-populate properties through Data Pages, any Report Definitions that need to report on this data will need to include explicit joins from the Case Type to the other tables holding those concrete Data instances.