I hate to disappoint, but unfortunately your request is anything but simple. At least considering our current architecture and the changes that would be required to allow for such a UI layout.
Right now, tab bars in Royal TSX are always tied to the tab views (beneath them). That means, at the moment there's no way to have the tab bar in a completely different container (the toolbar in this case) than the actual tab contents.
Further complicating the situation are splitted tabs. Even if we could separate the tab bar from the tab views, the split feature wouldn't work in that scenario. That's another reason why this request is not simple to implement. I don't currently see any solution for the split tabs dilemma except for completely disabling it for tab bars that are not adjacent to their tab views.
I'd love to be able to provide a UI layout that maximizes screen real estate even further but I don't see this happening anytime soon.
Open for suggestions though!
I have what I hope is a simple feature request. When working on my 13" MacBook Pro away from my desk and larger monitors, every pixel of screen real-estate counts. Hence, I use the Extended Fullscreen feature to great effect with Royal TSX. However, the tab bar doesn't hide in Royal TSX along with the toolbar, so while that's convenient for switching sessions, it is another toolbar taking up some precious vertical real-estate.
Would it be possible to get an option to attach the tab bar to the toolbar in Extended Fullscreen, such that the tab bar hides along with the toolbar, then they re-appear together when the mouse is pushed to the top of the screen? For an idea of how this would look and work, put Safari into full screen mode, then go to View and un-check "Always Show Toolbar in Fullscreen".
I'm aware I can get this effect on a per-connection basis by telling it to open in full-screen mode, but this has downsides, especially when multiple connections are involved. For example, a single connection in independent full-screen mode doesn't have a toolbar, so quick actions like favorite key sequences or commands aren't as easily available.