Even if you think what you would say is obvious, please add. This is genuinely something I think makes sense regarding local bus routes given the longevity of light rail and how infrequently routes change, but I also suffer from confirmation bias, so I’m hoping for reasons this would be a terrible idea but obviously would prefer reasons it would be an even more amazing idea than I thought.
Biggest drawback for anything on rails really, it works either really well or not at all. I think it is still worth it, but I am also incredibly biased towards trains.