It still raises the question of exactly what you plan to do data-wise that will require 40Gbit Ethernet. While I admit nobody knows what the future holds, we can make reasonable extrapolations. Word and Excel documents aren't going to magically ballon in size. It's highly unlikely you run a 100TB database on your home server. MP3's and even FLAC audio files aren't magically growing in size, and even some new fangled HD audio format an order of magnitude bigger wouldn't stress GigE. Your Internet connection isn't going to be 40Gbit anytime soon (and even if it was, your ISP is unlikely to provide an upstream link that isn't woefully oversubscribed). Netflix 4K streaming already works fine over typical 20Mbit Internet service. And as I stated in earlier posts, even Blu-ray's, which are the higest definition standard media currently available for sale (with no real successor in sight) peak at 40Mbit/sec with average bitrates well below that.
The only conceivable thing that's even remotely close to logical would be uncompressed 4k video editing. And most people do that off high-speed local storage array or, if you're a big boy, a Fibre Channel array. If you've got the need for a FC array at home...well, my hat's off to you. You're unique.