Well, I didn't thought of these. But about stable value, we determine it. We just have used to compare bitcoin with dollar. Imagine if there wasn't any euros or dollars. Just bitcoins. I think it would mean stable.
I think an ideal currency will never be a decentralized one. As we all wish that bitcoin is the currency of the world, we will never be able to achieve that since as long as it is decentralized, it will never be one. The value and the control, I think that is the reason why being decentralized is not a feature of an ideal currency, this is just my opinion though.