I think the small feature of being able to ride with a vehicle when on top of it instead of falling off when it moves would be a fun and meaningful addition to the game that just makes sense.

A ton of games already do this as it is simply just a fun a realistic thing that makes sense to happen. If you were to jump on top of a flat moving tank, would you expect to just magically slide off?

Imagine a scenario where you have just parachuted onto a moving enemy vehicle but it is completely unaware you are there. You ride with the vehicle as it moves and place C4 on it only jumping off to detonate it. This would be a very fun and possible scenario if this was introduced. As of right now if a player tried doing this, they would just slide off unrealistically which is entirely different to realistic expectations and can seem disappointing.

Battlefield is one of the VERY MANY games that have this feature and have had it for ages. In the attached video, a player rides on top of a friendly tank and fires an RPG from it, blowing up an enemy vehicle. I pulled this clip off of Reddit and the person who made the post found the moment fun enough to make a post about it showing that people can create fun clips and moments from this. I had to cut the clip due to BetaHub upload size restrictions.

For balancing reasons you should slide off of super fast moving vehicles or helicopters but a simple tank would make sense.