I think that there should be a clear distinction made between a decentralised economy, and a decentralised currency supply. The latter is what bitcoin is trying to achieve, and most other cryptocurrencies as well. Decentralising the entire economy is still unfathomable at this point, and it is unclear whether this is actually going to be practical or required. In the future, though, I think that what will happen is that centralised currencies will run in parallel with decentralised alternatives, to a greater extent than what is already happening. More people will most likely move their assets into decentralised, longer term store of values, as opposed to keeping them in fiat. However, the traditional financial institutions, central banks, etc. aren't just going to disappear off the face of the earth.
I have no choice but to totally agree with your assessment of things here. While we are dreaming of a decentralized economy, we have to accept that we are still living in the real world. The most likely to happen is the co-existence of the the current system we have and that one produced out of the use of the decentralized cryptocurrencies. Well, while there are frictions in between I am seeing that eventually things can be threshed out for good with many compromises along the way (whether we like it not we live in the world where compromises are needed to accomplish changes).