The iPhone entered a crowded phone market and now controls the vast majority of smartphone profits. There's really no such thing as market "saturation" when you can grow the market and eat old participants.
> First of all, it's a high price tag for them to get top talent in the area.
Apple has $250 billion in cash, so this doesn't strike me as a huge concern.
> Their success I feel depends on how much control they are willing to give up in partnerships…
As with phones, their hypothetical success in this area will be due to how much they won't give up. Apple learned this lesson with the disastrous Motorola ROKR E1, a.k.a. the one where they tried to be a "good industry partner" and play by industry rules.
If Apple enters this market, they'll play by Apple's rules and give up virtually nothing. Any launch partner(s) will profit, but on Apple's terms.