Regarding Quadro, their use these days is so niche that if you have to ask it is almost certainly not for you.
Almost no one buys them, because almost everyone who isn’t better off with a Titan is going to get a Tesla.
If I’m not mistaken the only difference between a Titan and a Quadro is RAM (and enterprise support I guess).
If you don’t need ECC or more than 12GB of ram there is no point buying a Quadro.
( Given the price of Quadros you could just buy more Titans rather than have enterprise support )
Problem is everyone needing high poly count and photorealistic objects seems to be using them, I remember speaking a couple years ago with the Audi Experience developer and he said it was running on 2 Quadros to maintain 90fps, also the aforementioned backpack only comes with that GPU integrated (and the alternative is a 1070 slower than a full size card).
Photo-realistic rendering can have very high RAM demands.
( they also can take many minutes to make a single frame in some cases )
For regular VR you do not need that much RAM.
You will need to know for your own needs how much RAM you should get.
For the backpack, if that is true, then I would guess that they are using a Quadro that is not as powerful as a Titan, but something more low-power.
They likely have a thermal limit or a power supply limit.
I used to use Quadro cards years ago for 3D CAD development. The main reason to use them was enterprise level support for drivers etc, you had a rock solid viewport in your CAD software with great anti aliasing and no artifacts of high detailed “wireframe” models. Frames per second was not their strong point though. Then I put in a top end gaming card and my viewport fps went from 45 fps to 120 fps so fully textured viewport animation playback was much faster.
If your use is Unity and Unreal then those are game engines and you would save a ton of money just getting the top end gaming card or a Titan as that is what the game engine is tuned to run on. However, If this is something you will deliver to your clients as a packaged arch viz app then you should make sure you target the min spec e.g. 3GB or 6GB of VRAM and make sure you do not exceed this in development. You could use a 1080 TI and 11GB of VRam and have very high detailed textures everywhere but then that would be a requirement of your clients to view it too.