You should be able to fill nested repeat grids with individual data. The topic has been posted before (https://adobexd.uservoice.com/forums/353010-adobe-xd-bugs/suggestions/13592076-texts-in-nested-repeat-grid-s-all-elements-chages) but did not receive a lot of attention. However I do see a lot of potential here, when working with complex tabular interfaces.
One simple use case I came across today is designing a calendar where you design a grid for the months in a year and an nested grid for the days in a month.