As my previous prototype was closer from a door than a window, why not try to design another prototype that really looks like a window this time?
Also, after reading about upcycling and fab cities   I'd like to reuse as much old hardware as possible. The idea is to recycle 6 laptops, each laptop screen acting as a "tile" of the window grille.

Hardware

The goal is to reuse old laptops that are considered too old to be useful by common standards. Those laptops could also be used as cheap Linux terminals, but in my experience, there are more available old laptops than people willing to use old slow aging computers running Lubuntu (which is a great project by the way)  
Another "master" PC can be used in addition to the other laptops if the video conversion and the webcam capture parts take too much time.
For this project to work, it is highly recommended to use identical laptops, because laptop screens differ a lot in luminosity, sizes, vision angles, etc.
So I will shortly be looking for local companies or public entities willing to get rid of old identical laptops.
If the PXE boot works, 5 of the 6 computer hard disks can be reused as an external storage. as  the video will be broadcasted, and as there will be no complex desktop applications, A 100Mbits switch should be enough to deal with the network traffic.
A webcam is required, ideally we would take it from one of the laptops, but this can be a bit challenging. If it is not possible, we will use an old USB webcam.   It must have a high enough resolution because we will display the image on 6 screens.
  If we remove the hard drives and optical drives and disable unused USB ports, the laptops will use less power and maybe we could use 5 PSU instead of 6? 

Mechanical part

This part will depend on the laptops I'll pick for the project, for example :
- How to attach the laptops to the window frame?
- Will the air flow be good enough in the enclosure?
- How far can the screen be bent? Can it be easily detached? 

Software part

OS
The plan is to use a very light live Linux distribution that won't need to be installed on the hard disk.
This way the system could just be powered off by a switch.

Boot
One "master" PC (one of the 6 "display" laptops or a separate one) will run a PXE boot server to allow the others to boot (like explained here)
Once booted, it will keep everything in RAM so it can be powered off without damages.
The bios could also be flashed to with an Etherboot payload

Sending the video
One of the laptops PC or a separate PC will be in charge of sending the webcam video on the network. Nothing spectacular here, we will just grab the video from the webcam and send it in UDP
Converting the unicast video to multicast
This PC will receive the video stream from internet and re-stream it to the other pc in multicast, without any processing to avoid too much latency.  All the computers will display one part of this stream but in full screen.
Another approach would be to use a high end network appliance running OpenWrt to do this part.
Displaying a part of a multicast stream.
This should be easy, ffplay or VLC should be able to do it.
 In VLC wiki, I found this line : vlc input --vout-filter=crop --crop-geometry=120x120+10+10
There may be something to do to have a good synchronisation, like using a NTP server to synchronize all the laptops, we will take care of this once everything else work!

So that's the plan so far!

After the holidays, I will contact Rennes'council to see if they are getting rid of old laptops or find a local company that does. If you know a company who's likely to get rid of 6 old laptops in the area, don't hesitate to PM me!