The problem for me is simply the rule of slots.
Similar to what another poster stated, it seems like a lot of the issues I have with new editions of rules sets happen when they make a goofy decision last edition, another rule interacts with this first decision causing imbalance or issues, so in the new version they rework ONLY the second rule, leaving the goofiness intact.
For me specific slots make no sense, which is why I love the EoM rule of TOTAL NUMBER of usable items...if you want to wear eight rings, with two on one finger, and there are no unstackable benefits, all perform at full power.
Granted, a limit of twelve items is also arbitrary and not supported in fantasy literature, but for me it makes far more sense than any system that causes your second necklace to cancel out your first. And it's easier to handle in story terms - "The character just doesn't want it or is too overloaded with magical items" versus "I already have a necklace and can't have another item that close - - yes, my magic cloak is in constant contact with my magic armor, but two necklaces touching cancels out the magic."
My fear is that what will prevent me from buying in to 4E will be stuff like this - - that EoM is nicely balanced and cool, but incompatible with 4E...if they've done something where having multiple rings IS unbalanced, then you're kind of stuck unless you buy into their rules for slots - - hopefully this isn't the case.
EDIT: Also - - I'm a big fan of the Mandarin, so obviously this is a touchy subject with me.