Been there, done that (pretty much).
I have a 40" TV mounted about 2 feet from my face when in the hood position. Works great to give a very “in the game” feel with Zwift in 1st person view (camera #3) and any POV ride videos too. The Field of View (FOV) is not perfect, but reasonably close and quite immersive.
If you’re running both TR and Zwift and have 2 TV’s in front of you that you want to broadcast them on, what is the best way to do this?
Several ways to do it, but I have a single Windows gaming PC, HDMI to the big screen and DVI to the small screen, 2 ANT+ USB sticks (one for each app), and run Zwift and TR. The screens are set for extended desktop, so I can move apps around and sideload music and web browsers.
Wow, even indoors my only constant screen in front of me is a 2,3in Element Bolt 
Stating at a brick wall, Eddy style?
It is a massive concrete wall… no bricks.
Props for that, I’d go mad 
That’s exactly my point. Notice they say “may need to…” and nothing concrete about any hardware limitations (which I suspect match Bluetooth specifications for something like 7 devices). The number of devices is limited by the software and how efficiently it can service the needs of each device. That depends on the nature of the device and iOS itself (which changes).
I’m just pointing out that a hard limit is mostly a myth (up to genuine BT hard limits of course). I don’t disagree that most people will experience similar limitations with similar equipment. Most trainers are also serviced as one BT device by iOS even though they have multiple data streams for power, cadence, control, etc. Combine this with the BT capabilities of a smartphone and there are plenty of streams available.
That all said, I think I would prefer a native tvOS TR app as well but hard to way without trying it. Mirroring is a little less convenient but works just fine (better if workouts would lock to landscape during the workout).
Hopefully the next iteration of Apple TV is powerful enough for there to be none of these issues.
