I've been intermittently working as a sales girl in Selfridges since 2011 (great extra money for a student!) and it wouldn't surprise me if the Apple Watch location in the Wonder Room is only of temporary nature. Many booths there are rather temporary, ie in fall 2013 we had a stall for the Dom Perignon x Jeff Koons collab (the balloon venus) for about 3 months until another novelty replaced it. Sometimes there is also a theme for a couple months: I remember for instance a "white" theme in winter 2011/2012, where they showcased all sorts of luxury goods ranging from white jewelry, over a white Hermes Kelly Bag (for about 40,000 £ if I remember correctly), to white-themed artwork, white fur, white designer shoes with diamonds etc.
It would certainly make sense for Selfridges to showcase the Apple Watch Edition in their Wonder Room while the hype is new and also for Apple it's certainly a great idea to give the Apple Watch Edition an initial boost in Selfridges. However, I'd doubt that it's going to be in the Wonder Room forever or generally outsourced from the Apple Stores. I think once the initial hype has passed, it's going to join the rest of the product range in the Apple Stores.
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