I'm sure there will be teleportation tweaks if it doesn't break your immersion when a companion teleports to you. I've noticed the companions jumping down small rocks but never over cliffs (The game actually teleports them if they end up in a programmatic world of hurt but its the last option)
Game already teleport follower to you at load doors, add that if follower is to far behind teleport her 5-10 meters behind you.
I had a mod with a call horse spell, it worked nice except that outside cities the horse might end up behind the city wall. This would be less of a problem with an automated script as follower would simply teleport again if spawned in an closed area.
I would also want some standing orders to followers like ranged or melee, keep close or keep some distance, and activity, engage enemies in range, do not start fighting before me, wait until enemy is close before fighting and just defend yourself.