TL;DR
Adding memory to trains which can be set and read by the circuit network, increasing automation and creating novel gameplay.What ?
The memory can only be read/set when the train is at a station. Other than that, I'm not sure implementation details make much of a difference.Why ?
Main reasons:- allowing automation of something which can currently be done manually
- completing the trifecta of train control (station, schedules, trains)
- novel game feature: allows the creation of a discontinuous circuit networks, with trains acting as a 'postal service' to tie them together.
Automation
Currently, if you want a specific train loaded with specific items, there are two approaches: a) set filters on the wagons, which is prone to jamming and is laborious to change and b) use circuit network to remember a train ID and load items based off of it, which could probably be automated with fiendishly annoying circuitry that's not really practical for most players.
Whereas if the train had a memory cell, it could simply carry around a list of the items it wants. Need to change that list? No worries, have all the trains cycle through a station which can alter that list to whatever you need it to be.
Decide that all your outposts should offload different items off of your supply train? No worries, the supply train could carry the most current list for them to update off of.
This seems elegant to me.
Train Control
Roughly, currently schedules control where, stations control when, and trains can (poorly, with filtering) control what. Filtering is an adequate solution in the early game, but simply doesn't scale: the train cannot communicate its filters to the station, and the filters can only be changed manually, one train at time.
We currently control 'what' through a combination of where and when, but train memory would allow a higher form of train logistics: imagine a train stopping by many outposts, remembering what they all need, stopping by the base to pick up only the necessary items, and then offloading the correct items in the correct places.
Can you achieve something similar currently? Yes, but only with a lot more manual work and less precision.
Novel Gameplay
Currently, its not really practical to have separated circuit network talk to each other. It could theoretically be done by trading physical items and have that be translated into some quantity of pulses, but at that point it'll just be easier running a wire.
But if trains had memory, you could have a distant outpost communicate with the home-base circuit network, without needing to run a cable in between. A wild-west era post system, with brave messenger trains weaving their way through hordes of biters. Applicable to all cases? No. But it seems elegant and cool to me.
Conclusion
Yes, many similar outcomes could be achieved by using more stations and interesting scheduling, but with changes and additions requiring lots of manual intervention, i.e less automated than an logistic bot network.
And while a similar effect could be achieved by essentially creating a base spanning mini-computer, this is simply not achievable for most players (how many current factorio players are comfortable with multiplexing?), and personally I hate the aesthetics of dragging a circuit network everywhere.
In short, I think train memory could be an interesting addition, that doesn't eliminate any of the current puzzles in the game, but presents a challenge in and of itself, rewarding the player with otherwise unattainable functionality.
