In version 0.9.6 if you try to attach a playable character to something like a vehicle and then drive the vehicle the player is stuck in the original position and has no movement controls anymore.

It would unlock vast possibilities for gameplay if players can be linked to other entities while still being able to control their character. A system for this was introduced to DayZ as part of scripts\3_Game\human.c

proto native void LinkToLocalSpaceOf(notnull IEntity child, vector pLocalSpaceMatrix[4]);
proto native void UnlinkFromLocalSpace();

With such support, it would also be important, that jumping, vaulting/climbing obstacles, and using ladders to get onto a moving entity or traverse a larger moving entity (start and end point on the moving entity) are possible. In DayZ this was solved by first requesting the link to the parent before performing the player command such as vaulting or entering the ladder.

The functionality could be used for players walking freely on cargo trucks to fight or other new vehicle types such as trains: https://youtu.be/bYybLo1LpmU?t=57