A DIY modder has made a nice change to his Nexus 5. He was able to get 64GB of internal storage on the device. He did so using an eMMC 5.0 chip and soldered it to the motherboard. The phone didn't fully recognize the storage right away, but all he had to do was tweak some software to restructure the partition tables. It's a dangerous mod that could break your phone, but if you are interested in trying it yourself you can find instructions at the source link.