they need to be bigger. Trains with a block count of 1500 are still fairly small (it's only the size of 2 and a half max size trucks). Not only is this not realistic but it also limits the applications for making some awesome trains which is probably why they're not widely used. If they were larger it would allow much more detail and you could create carts that people can walk around instead of just carts for the purpose of making the train function. you could also make detailed and high capacity cargo trains which could even transport trucks around.
People hardly ever use trains and bigger ones would be very cool and could be a good alternative for trucks or even cargoships. even an increase to 2500 blocks would be a huge improvement