Interesting request. I'll consider it but I don't promise when I'll do it (or if ever).

To do it automatically I'll have to expand the TDIMode property from a boolean to an enum like ntTDINone, ntTDIControls and ntTDIForms.
And then, detect when a form is going to be shown modally or non-modally and place every non-modal form in a tab (with the SetParent API), and allow modal forms to display normally. Probably with a CBT hook.