Here are some ideas that I came up with to add more progression and to add more usefulness to IR in earlier stages of the game.

1. Iron or wooden parts only. Train and rail parts are crafted on a small, multiblock table/forge (probably 2x3x1 or something similar). No power required, although there is a lengthy pause during crafting. Some materials lost in the crafting process compared to more advanced building methods.

2. Works for all parts. A version of the iron/steel melter that is directly heated by burning fuel. Slightly altered versions of the other machines that are powered by piped-in (fluid) steam, including a proper steam hammer. Slower than the electric machines, but cheaper to build.

3. Current, electrically powered IR machines.

Additionally, add locomotive and car blueprints that must be unlocked with XP in order to build that locomotive or car- a greater cost for bigger locomotives and even more for advanced ones such as diesels or electrics. Alternatively, resource pack creators could set their own blueprint costs.