PluginGuiWidget can't dock to viewport tabs?

[Tiffblocks]

Ability to dock lua widgets to main view

I would be inclined to implement this as a new way of creating Plugin Guis. We already have CreateDockWidgetPluginGui to create plugin guis in dock widgets. We could also add CreateTabbedDocumentPluginGui (what you are describing), CreateDialogWindowPluginGui for dialogs, etc. Not on the roadmap now but we did deliberately design with the expectation to expand in this direction. Maybe something for a summer intern to tackle.