Add the ability to assign color to tasks.
Easy accessible color palette with a few presets + custom colors, so it's much easier to get an overview over tasks. I.e: shopping list: Green vegetables, Blue fish products, Red meat products..., or Green outdoor tasks.. Wunderlist is great for shopping/packing lists, but it takes too much time reorganizing and fine reading long lists..
I was going to put in a suggestion similar to this (add a prioritizing feature, e.g. 1-5), but this would provide the same effect.