One of the things that really stood out for me back in the day when I played Phantasy Star 2 on the Genesis was the way your party members would follow around behind you, but there are a few reasons why that wouldn't work so well for Horn and co. in LOTRO. Here are a few of them:
1) The way that pets work means that we can set a displacement for them from the player's position, and they'll try and maintain that distance. When you're dealing with four pets, you'd need to set the displacement for each one separately, which means that maybe Horn is right behind you, and Gleowine is ten feet back or so to give room to the other characters in between. If we want to be more realistic, we'd really need to have multiple versions of each pet composition based on your quest state, so if Gleowine is the only buddy you have tagging along, he'd have the least amount of displacement -- otherwise it would feel like he was stalking you from a safe distance!
2) If you have four of these pet buddies tagging along with you, that's four whistles taking up space in your inventory and they'd need to be indestructible so you couldn't delete them -- deleting them could have adverse effects on the associated quests.
3) Under-the-hood, there isn't just one Horn, and one Nona, so every quest that involves them would need to be reworked so you could interact with the pet buddies for every quest. That would require so much structural work that anyone currently underway these quests on the Live servers would lose their progress on the quest and have to re-acquire it, which isn't ideal. Furthermore, there are many times when we vector you to a location to talk to one of these characters so you'll be near the next spot you need to be, either for gameplay or story reasons. If you can advance the quest by talking to the pet buddies, there's no guarantee that you'll be near the location we expected you to be.
4) EDIT: I thought of another one. If we tried to hide the pet buddies on the client, when you're on a step where you can accept quests from your own pet buddy, you'd likely see everyone else's pet buddy for that quest as well, and could accept quests from their Horn or Nona as well. That's not great!
I think that it's a neat idea, and I like when games do this, but I think in this case it wouldn't improve immersiveness that much.
MoL