It would be nice to have the Tabs being Tab<T extends Node> where T specifies the content node.

Of course, this would influence TabPane also, especially in
ObjectProperty<SingleSelectionModel<Tab>> selectionModel property, which I would expect to be an ObjectProperty<SingleSelectionModel<Tab<T extends Node>>.

Part of the discussion will propably be why the container of the tabs (TabPane) needs to have knowledge about the content of contained tabs, especially as it is treatened like a black box. Though, benefits would mostly influence missing typecast which could be avoided then, especially by a

T Tab#getContent()

call.
Having the need for different tab contents which can't be fused to one T within a TabPane won't let us loose anything as T as at least a Node anyway.