In what way are the demands of an idler drive different from, say, a belt drive? I haven't used one in decades and never thought about this when I did use one. Do they generate more internal vibration than a belt or direct drive? If this is the case then would they be better off with a fluid damped arm like the V? If the vibration is not a problem then I can't see how you would be limited in your choice; just use the one that best matches the cartridges you like.
