I just found the mod Junk Train (https://mods.factorio.com/mod/JunkTrain2). It introduces very cheap (and very limited) rails, stations, signals, and trains as soon as Automation has been researched. I believe it would fit in wonderfully with Bio Industries, providing old choo-choo-trains (that could be fueled with wood from the Bio farms) driving slowly over wooden rails. Seems perfect for prolonged early games: I've generated my map with low-frequency, poor coal patches so I can take advantage of Bio Industries' wood-to-coal production line, and I also play with Research Causes Evolution, so it will take me a long time until I'll research normal trains.

Now for my suggestion:
Junk Train has this recipe: 1 Wood + 1 Stone + 1 Iron stick --> 2 Scrap rails. Bio Industries has 6 Wood + 6 Crushed stone + 1 Steel plate + 1 Iron stick --> 2 Wooden straight rails. It also allows an update to regular rails: 3 Wooden straight rails + 10 Stone brick --> 2 Rails.

Could you deactivate the recipe for Wooden straight rails and make the update recipe more expensive if Junk Train is installed? It doesn't make sense to have cheap and expensive wooden rails -- but the convenience of having very early access to trains should come at the price of an expensive update. Given that 1 Stone --> 2 Crushed stone, I would suggest this recipe for the update from Scrap rails to Normal rails:

1.5 x (5 Wood + 4 Stone + 1 Steel plate) + 3 Scrap rails + 10 Stone brick --> 2 Rails

The term in parentheses is the difference between Scrap rails and and your Wooden rails, so you'd actually apply an upgrade Scrap --> Wood --> Normal. The factor is to account for the 3 Wooden rails in your upgrade recipe. Because recipes must use integer numbers, the actual recipe after rounding up would be:

(8 Wood + 6 Stone + 2 Steel plate) + 3 Scrap rails + 10 Stone brick --> 2 Rails

Would you consider this idea, please?