I've always been intrigued by making things faster, better or more efficient and one of the things that's really excited me recently is the theoretical "diamond age". A time in the future where diamond becomes so cheap to produce that it can be used in everyday applications. Laptop heatsinks for instance, lighter than copper and conducts heat 5x better. Although why stop there, the entire laptop could be made from diamond and the case can be the heatsink at the same time. Hopefully one day there will be an open source 3D diamond printer we can use to bring this into reality.
Diamond Heat sink 3D printer