There is a rough implementation available based on gobject and gtktreeview implementing a custom gobject structure.
https://github.com/chergert/custom-gtk-widgets/tree/master/eggsqlitestore

IDEAS: ===========================

• use eggsqlitestore, but do massive improvements
• only load on-demand 1000 lines into the treeview
• use signals for resize/scroll to calculate the lines to load/display
• on a scroll, disable the widget and load the lines when the scroll is finished
• discard or cache all other lines up to a limit of X MB cache
• use a simplistic view, just consisting of headers, listen for change in prefs to reload the appropriate lines if the layout has changed
• on a row expand cache the sub-thread lines and append them to that row
• drop pantreestore in favor of the new model or not?
• pantreestore could still be useful, but the information about the other articles isn't readily available
• pantreestore/groupheaders need those informations sometimes, so a workaround is needed(!)