This log started as a comment but I think it now should be a log. 

About an hour after writing this log, I was scrolling Yanko Design and find out about the Grab Shell keyboard. Both the name and the keyboard look like it should've existed in 2003 (and from an anime of that time). 

It looks clunky and heavy. I checked the page and it indeed is clunky and heavy, coming in at 220x160x40mm (thinnest) and 0.95kg. Unfortunately it also costs the same expected BOM of Tetent (and looks to be more expensive after the preorder window).

I read their story and I agree with the points mentioned, such as:

• Robots are usually developed and tested where a desk / flat surface is not available.
• CAD designers need specific and variant ways of controlling the software, and a mouse+keyboard alone is not enough.
• Wanting to use multiple devices to write thousands of words a day, even when lying down.
• Play Minecraft and Trackmania (with console level haptics) and have a solution that can be used in VR.
• Not be afraid to Invent Everything Here, even if the solution can be seen as suboptimal.

It also lead me to discover TrewGrip (and now I'm not sure why the Yanko article says it's the "worlds first"), which looks to be the QWERTY equivalent of this Tetent concept. Unfortunately, the kickstarter failed and so "contact us" sounds like the only way to get one. Why couldn't I find this when I was spending months looking for every input device recorded on the internet? No idea. What other products are out there on the internet that I don't know about? 

Well I actually went and found out other rear-facing keyboards.

Firstly, there's what seems to be a concept, AlphaUI Twiky:

Microsoft Research had a go with the RearType:

Hackaday also featured a modified keyboard.

What I can tell from all 4 of these is that it seems to be intended that the screen is on the same plane as the keys. For viewing the screen and typing, my wrists do not agree with that assessment (unless my arm is fully extended and straight), and this is the reason why the screens on Tetent Concept3 are placed where they are.

What have I learned from this?

[ breathes in ]

Me to Future Me: 

JUST! SEND IT! 

Tetent [Concept3] is the most FULLY FEATURED (but ergonomically unverified) keyboard equivalent known on the internet. 

IT'S GOOD MA GUY! Just BUILD Tetrinsic and know ONCE AND FOR ALL if the chain slides nicely and the multiple force levels can be actuated without errors, ok? 

You've gone though 3 COMPLETELY different concepts spanning over an ENTIRE YEAR. 

It's DESIGNED to type faster on ONE hand than practically everything else using TWO. 

IT. HAS. LCD. ANIMATABLE. BACKLIGHTS! Can't see 'em [when in use]? DOESN'T MATTER. Alienware laptops and LED phones exist. You can ELECTRONICALLY change how the keys LOOK AND FEEL!

It PHYSICALLY... MOVES YOUR FINGERS... TO TEACH YOU!! Honestly only a direct-to-brain download could beat that.

You don't need to lift your fingers to move to another keyboard-key-equivalent. Just slide over. Remember reading about all those people that hate the idea of touch keyboards because they have to hover their fingers? Well they have to do that with their keyboard anyway or risk a finger getting stuck in the trench between keycaps.

You can type while walking! And hopefully #TaskPercent [gd0140] can be written for it, allowing you to take notes on the go.