You can't stand on boats because they're entities, it'll take a lot of extra programming and problem-solving to make that work. They'd have to have it transform between a solid block and an entity, or find a way to make an entity hitbox partially solid. Not to mention fine-tuning that would be a nightmare, you'd have boats overwriting/removing water and blocks, or boats getting hit by other entities and not moving, etc. I'd also like to see them add that, but it's probably a ways off.
And the crash is because it's an unstable build, you tard.