First question is easy: yes, the widget tree can be updated. That's generally done by diffing data stored in view nodes, but in fact the View trait is open-ended and you can implement the rebuild method to do anything you like. And yes, selection state lives in widgets and it is absolutely a goal to have that persist.

The second question is more challenging (see the "advanced topic" under identity for a little more background). View id's cannot be re-parented, in other words when a parent relationship is expressed in an id path (by virtue of having the child id follow the parent in a path), that relationship cannot be changed. However, widget ids and view ids are not necessarily the same, though they can be. I think what's needed for your use case is a level of indirection so the view id paths remain stable, but the widget id structure relationships can be changed. I haven't worked out all the details, but think it can be done, and if it's done right it wouldn't require any rebuilding of widget subtrees.