I would really like this feature. See my "Private Markets" group, which contains the subgroups Fund Performance Forecasting, Private Equity Fundraising, Secondary Private Equity, and Venture Capital.

To resolve positively, any subgroups that Manifold creates would need the functionality of automatically linking any subgroup markets to the higher market in the grouping (i.e., any new market in "Secondary Private Equity" is added to "Private Markets").

Discussed in this feature request post.