I would like to suggest locomotion as a sub component of the 1.18 update, whatever it may be. Many tools for long distance travel have become mostly unused because there are faster, more convenient methods, like blue ice and nether shortcuts. I’m proposing improvements to horses, boats, and minecarts to make them more useful.
For horses, add horseshoes that can be made of different materials and are enchantable. Shoes for speed, jumping, damage resistance, and moving through water would be the most useful. It would be nice to explore the countryside on a horse without having to get out a lead or build a bridge every time you come to a river. Enchantable horse armor for taking your horse through the nether would be nice, too. Give the horse knockback resistance so that ghasts can’t knock it into the lava without destroying the ground beneath it.
For minecarts, make them capable of being used like small trains. Create an armored minecart that smashes mobs and certain breakable objects that it slams into. Restore powered minecarts, and make the type of fuel affect the speed of the minecart so that the fastest minecarts are almost as fast as boats on blue ice but a lot less tedious to use on a large scale. Give the ability to link minecarts to Bedrock, too, with one powered minecart able to move a set amount of carts.
Boats would need improvement, too, but I can’t think of many ideas other than adding an iron boat that is more durable but sinks if it’s broken instead of floating like most objects on water. Maybe add a large boat that is slower but can haul larger mobs like horses and golems or large chests
IDK about Horse Shoes, I think just making Horse Armor (or saddles, either one) enchantable and adding a few new enchantments for that purpose would be adequate. The ability to slap Frost Walker on Horse Armor in particular would be very useful.
Minecarts need a more extensive overhaul IMO. They're not bad but just take a lot of investment for a form of transport which isn't overly efficient. It's AFK friendly for really long distances, but again--lots of investment. Your ideas aren't bad by any means, but I personally would like to see even more in-depth attention given to them.
Boats don't need much IMO. Maybe a steam motor that can be put in a boat at the cost of the second seat, and then obviously we're getting chest boats whenever the Swamp update drops. Other than that, they're pretty adequate for what they're meant to do, and the only suggestion I can otherwise make is for Crimson and Warped boat variants
Improved mine carts and horses could be used in the nether but require greater preparation than they'd need in the overworld, like constructing safe tunnels and bridges to avoid lava pits and ghast fireballs.
Redstone contraptions and music disk players already push the medieval fantasy theme to its edge. Powered mine carts that still look like mine carts, not locomotives, wouldn't push it much farther. If the impact of the armored mine cart caused knockback but not a lethal hit except to weak mobs, it would be less likely to be abused, too.