What I expected to happen was...:
In 1.13 riding a boat into a end gateway block with a command specified teleport target would teleport the boat and player to the target coordinates.

What actually happened was...:
The end gateway block registers that an entity enters it but does not teleport the boat until the player dismounts it.

Steps to Reproduce:
1. Create an end gateway in a flat-world with the command: "/setblock 0 10 0 minecraft:end_gateway{ExactTeleport:1b, ExitPortal:{X:0, Y:10, Z:10}} destroy".
2. summon a boat with command: "/summon minecraft:boat ~ 10 ~ {NoGravity:1}".
3. Right click boat to ride it, and drive it into the end gateway collision box.