I like the concept, but at some point, those features will have to come together. By creating completely different timelines, bringing them together gets harder

I like the concept, but at some point, those features will have to come together. By creating completely different timelines, bringing them together gets harder as harder as each of those progress in time. By using a single timeline, where features slowly come together while not being complete, you can see how they interact together since the beginning, which might be crucial to their development. I think the ideal is a mixture of both strategies, a single timeline where working increments are added, and different timelines that exist only to work on small changes that are eventually joined (even if not complete! they just need to "work").