Gamedev wohoo! Welcome here!
There is also the solution of using a detail view, in which you can reference as a lookup some tasks displayed as table.
For example, you create a table features. You create another table called tasks.
In the task table you add a column lookup to the features. Each time you add a new task, you associate a feature.
But, in your feature table, you add a column called tasks with a formula like : Lookup(TaskTable, Feature, thisrow)
Then you’ll have all the tasks associated with the feature.
Next, if you change the feature table view as detail view, and edit the layout, you could set the Task field as a table.
With this solution, you can work on the tasks of a feature directly in the feature table.
There still need some polish about this detailed view, I think that the sub table is too narrow.
Personally, I would also love to be able to display those sub tables in a regular table.