A few months ago I had a ghastly time trying to take a bike along with me for a multi-stage train journey across the UK. Trainline is good about abstracting away the (pointless) differences between the train operating companies -- it's just a single interface and you never have to know which company operates which section of the route. But this abstractions breaks the minute you want to bring a bike on board -- you need to contact each company separately, and each one has its own bespoke and annoying way of doing it. Some by phone, some by email, some through their website (that you need an account for), some by social media(!). So I emailed Trainline's customer support saying how lovely it would be, if bike reservations were as seamless as people reservations, and to pass along the idea to their dev team.
Lo and behold, while booking a journey the other day I noticed a new option for bike reservations on the route planner interface, that I'd never seen before. I haven't had opportunity to use it yet, but I hope it works well, and I'd like to think that it was my email that tipped the scales into it getting implemented (Lord knows I can't have been the first to ask for it).