TW has already "tabs"
in the Bible search view
but it has no tabs
in the Book Search view.
Thus showing at least that it is possible,
to have tabs in TW even as of now.
but if you would add TABS as a feature,
then one could have multiple book searches open in parallel
(instead of them taking up huge screen space
by each one being only a dockable window
and although one can minimize them
it also is not a real profitable way)
and then furthermore with Tabs
one could thus "pre-load" these book search windows "with a search term"
and have them thus as kind of TABBED saved searches with results open
and then view-able at any time thus stacked in tabs, with just a single click
(and maybe another single click to just re-fresh the search results again)
and so tabs would be useful for an even greater split-windows organization.
And since again you already have it possible in the Book search
it should be not so hard to implement it also for the rest as-well.