Can a minecart junction automatically configure based on something chosen in the originating station without command blocks?

You cannot test for an item in a players inventory by using only redstone (without killing the player).

However, you can have a chest minecart that moves in front of the player and check the contents of the chest.

This is what my test track looks like:

The minecart will follow the chest minecart in a circle indefinitely unless you put a paper into the chest minecart.

Here is a better view of the starting area and where the minecarts stop:

Minecarts appear to be a bit buggy when they are close to each other, this setup for starting seems to put the minecart a good distance behind the chest minecart.

Here is the junction itself:

When the chest minecart goes over the hopper, then the hopper will try to pull a piece of paper from the chest minecart. If it succeeds, then the chest minecart and the regular minecart with the player inside will both leave the ring track, the chest minecart will go past the hopper again and get the item back, which resets this junction.

For this to work you need to set the hopper up like this:

You can use renamed items for this, so it would be possible to use papers named after the destination of where you want to go.

Note: this setup may vary a bit depending on what direction you are going. In this case the junction leads to the west.

Note 2: I don't work much with minecarts and rail systems, there may be mechanics in place that I didn't account for that would make this fail in some situations.

I habe build exactly this contraption back in 2017, but it is a Redstone mess under the Station and it was hard work to secure it against user error.

https://wiki.natenom.de/minecraft/schematics/2017

It's based on the idea that a ticked in a Chest Cart in front of the player is read out at the switch with an item filter.

My Friends keep braking it and I lost interest because I have no one to play with.

Reconstructing the part in survival mode is a pain in the ass, and I would love to rebuild it with a Minecraft professional to make it easier.

I'm sure I haven't considered all the Redstone logic circuits.

This might give you some ideas...

Benefits of this design.

1. You can replace the complicated station selection sytem with the player manually putting x number of items in the minecart_with_chest to travel x number of stations.
2. You can make it a loop rail system so that the second journey doesn't need to be back to 'home' station, you just move x number of stations around the loop.
3. The number of stations is only limited by the number of items you can fit in a chest.
4. You don't need to 'follow' the rails with a line of redstone to transfer the signal.
5. It is possible to have 2 players on the same stretch of rail but each going to different destinations. Items in chest can be 'payment' for travel e.g. 3 iron nuggets to travel 3 stations