Ideas that are too old (too many things have changed since) and ones which won't be implemented for certain reasons or if there are obviously better suggestions.
Nope. It is just complexity for complexity. At the time you have blueprints and construction robots you can place blueprint to have them build easily with any extra equipment around. Manually placing double railway would suggest it is intended way of building rails when single railways are quite good when having single train in some isolated cases. Also that approach would not allow placing curved rails so the rail planner would be useless and with no gap in between it would be forcing the right-hand-side signalling which is not forced by any means in vanilla.