I have a suggestion for the train controlling.
Connecting a "Reader" to a track reads whether there is a train in the block (i.e. whether a signal facing into the block would be red).
Connecting a "Reader" to a signal reads whether the signal is red.
Writers could have two conditions for two different "levels" of how much they affect the train network.
Connecting a "Writer" to a track, at level 0 does nothing, at level 1 makes the game behave like there was a train on the track (so that signals leading in become red), at level 2 makes it like that the track didn't exist (so trains don't path through that track piece).
Connecting a "Writer" to a signal, at level 0 does nothing, at level 1 makes the signal behave like a chain signal, at level 2 turns the signal red.
I believe with these you could make fancy prioritisation or time-division signal systems, which is something I've wanted to do for a while, as well as make a safe at grade crossing (manually switch constant combinator -> turns signals red), and just generally be able to have the factory react to a train showing up.
Also +1 to whoever it was that suggested calling them "sensors" and "actuators".
Also also, they should be able to connect to gates. Readers tell whether it's open or not, writers force it open (or force it closed).
Also x3, the newspost mentions turning belts off and determining number of items on belt. Does this mean just one belt square, or the whole line of connected belts (traversing corners but stopping at merges/splitters/side-loaders/perpendicular underground belts)? Because the latter would be much more useful than the former