If I don't go for the Rapha I'll most likely go for this. Will be perfect for my road and MTB adventures.How about the Sportful Fianre No Rain Top? It just about folds down to fit in my Jersey pocket, it's wind proof and water resistant.
Re the OP, I don't think you will find a "packable" softshell. I have a few different softshells and the lightest warmest and thinnest is a Gore Oxygen. It is way to bulky to be considered packable though. The best compromise would be to wear a winter jersey and then stick a wind proof packable jacket or gillet over the top. This is cost effective and allows you to layer for changing conditions.