I don\'t think the follow command would be a bad idea, in reply to the having two options why make a third that renders the previous two obsolete. I think that\'s an overstatement. There will be time where a GM will need to be somewhere and visible and chat with the parties involved. This is pretty standard from my understanding, so the teleport command would always be useful. Invis, well that explaines itself, and is essentially made so you could follow people without them knowing.
As for the follow command, there are many games that implement it for players not just GMs, for example when people group into a party, and one person is leading, then the rest of the party set to auto-follow that player and in that way don\'t get lost (I think FF XI has this). For a GM, all you would have to do is add a teleport statement and invis statement before engaging auto-follow.
As for the difficulty in coding... Well, I\'m not really an experienced game programmer, but IMHO it would not be that difficult (comperatively speaking), especially if you make it a GM only command that simply *intercepts* the players position coords and places the camera there. So essentially the GMs client is asking for that players coords to observe him and essentially follow him.