It would be nice to have a type of block that when laid in a rectangle would act as a big screen, and have a couple of variables inside to control background and foreground color for rendering text (much like a screen of opencomputers or computercraft)

Yep, but it's not on the roadmap atm.

You're welcome to prioritize this one via https://www.patreon.com/kroeser though.

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is this idea still alive?

Related: #334

Something like this has been on my mind since I first implemented the Display Panel.

Definitely possible to do, but not very simple due to the multipart-nature of this mod.

Perhaps some time in the future.

Something like IC2 Nuclear Control maybe? with a Master part thats configurable, and slaves that only increases the size of the screen...