Isn't Kensington & Chelsea due to be part of the Congestion Charging Zone any day now? Maybe driving in won't be so advantageous to many people?
As far as organic and local foods go, it sounds as though they're only going to use what they can get, if they can't get it in the UK, then they'll go to Europe, if not there then anywhere in the world. I suppose the whole organic farming business, while taking off can't possibly supply all organic retailers anywhere near 100%. With much more competition in this arena in the UK than the US it may be even harder for Whole Foods to get as much organic, local produce that they'd like.
Having said that, given its reputation as being pricy (ie "Whole Paycheck") they might aim to pay these producers more than the likes of Tesco and may be able to get them on board, if the customers are willing to pay more anyway.
It's a big gamble to have 80,000 square feet of this type of shopping, we'll have to see if they can succeed.