A heads-up to those like myself looking out for the physical version, it looks like it's starting to crop up on sites that aren't the Nintendo Store, so keep your eyes peeled.
So far I've spotted it for £42.85 at Hit (the recently rebranded Base), where I'm sure it will come down closer to the £35 RRP in the next few days, but I've gone and put my pre-order in with ShopTo, where it's only £29.85! Hard to imagine you'll be able to find it for much less than that anytime soon
EDIT: also, as if we needed anymore confirmation of Metroid truly being back at the fore for Nintendo, there's now a dedicated Metroid portal on their official site!