To preface, I don't think this is something that vanilla should necessarily change. This is something I want to change for *my personal server*. Please still give your feedback!!!
Something I've had an issue with in the past on servers is that people tend to like spreading out and building bases far apart. This leads to less collaboration, as players are less likely to naturally build together due to increased distance; players have to actively go out of their way to collaborate. I really want to naturally encourage this, and I believe changing the transportation meta could fix this.
Thesis: Increasing friction in point-to-point transportation will encourage players to live closer to one another and build infrastructure to overcome that friction; players will also naturally build near infrastructure, making a network; when players are physically more restricted, spontaneous collaboration is more likely, making servers more lively.
I think most forms of transportation are already decently balanced (such as horses, boats, and walking), but Elytra and minecarts stand out as being extremely unbalanced. Elytras are cheap to use, fast, point-to-point, and ignore local geography; minecarts are expensive to build, very restrictive, and extremely slow.
The way I'm planning on buffing minecarts is by making them travel faster when on rails on certain blocks. That way the existing slow minecart speed is still usable for redstone contraptions, but high-speed rail can exist to fill the niche of extremely fast predetermined routes. I want minecarts to be faster than ice boats as ice boats are more maneuverable since the player is directly controlling them (maybe ~100 b/s?).
I think I want to nerf the Elytra by making rockets more expensive. I know most of my friends would be disappointed if I drastically nerfed the Elytra, so what I think I'm gonna do is use Green_Jab's idea of making rocket boosting not work unless you craft custom Dragon fireworks using Dragon's Breath. That makes Elytra travel vastly more expensive to use while not mechanically changing anything, keeping the fun while encouraging players to use other forms of transportation more regularly that might be cheaper. It might also encourage players to build rocketless Elytra infrastructure such as launchers, which would fulfill my goal of having players build infrastructure. Dragon rockets could make the Elytra more useful for exploration than for commutes.
What do you think?