Solving the scaling issues with Bitcoin would be awesome and sidechains would be an excellent addition as well. To be the perfect crypto, true anonymity would be great, but this is probably not something most mainstream crypto investors care a lot about. It is the investors and speculators that are driving the price of Bitcoin at the moment. If this ever changes, we will see more practical features like true anonymity and maybe some kind of basic smart contract, though I like that Bitcoin is a "store of value" only.