I love the building but the surrounding area is ground zero for grotesque property speculation in London. Recently it looked like the developers had overplayed their hand and wouldn't be able to shift all the £1M+ flats - but now with a bunch of Apple devs looking to rent them out, who knows?
Also, important to remember, Apple is moving their HQ, not adding a brand new location. The majority of the people working in that office already live in London, so when they moving in to pricey flats in Battersea, they're moving out of similar priced flats elsewhere. While possibly a windfall for those particular developers, the overall supply/demand situation in London won't change much.
Most of Apple's current offices in London are based in or around Regents Street, nobody is living in apartments near there. Most people are commuting in already, so it's not a massive upheaval.
More than likely a couple who are already earning ~£70k/year each probably already have some equity in a current home, so a £1m home might not be much of a step up for them.