Communities are more than what currency they are using, whether Bitcoin or cash or debit/credit cards (considering a debit/credit card as a proxy for cash). Thinking about what makes a currency useful there are a couple of important characteristics: stability of value, portability, and acceptability for transactions.
Bitcoin fails on two of these at the moment, stability of value and acceptability. Acceptability is improving as more people are willing to accept Bitcoin as a currency.
Because Bitcoin is a peer to peer currency and digital and pseudo-anonymous Wikipedia topic Bitcoin. So it does have characteristics that are attractive to people who want to be as independent as possible. And there are crypto-currencies other than Bitcoin The 6 Most Important Cryptocurrencies Other Than Bitcoin and it appears at this time that since the value of these currencies vary depending on the Bitcoin market rate and that Bitcoin seems to be a kind of commodity, it will probably remain fairly volatile in value. See Meet the millennials making big money riding China's bitcoin wave.
What provides national currencies such as the dollar and the euro their reasonable level of stability of value is the central bank. One reason the US created the Federal Reserve was to provide stability of value, History of central banking in the United States.
The characteristics of sustainable communities (see Wikipedia topic Sustainable community and Sustainable Communities at HUD ) tend to be different for different people. The main principle most agree on is Sustainable living however what that actually means varies depending on the community being discussed.
"Decentralized community" is actually a pretty vague term though this paper, Decentralization and Community Empowerment: Does community empowerment deepen democracy and improve service delivery? has a nice discussion on the concept and how it promotes a more egalitarian society.
A decentralized community is not necessarily more sustainable in terms of reduced ecological footprint, carbon and other emissions, etc. Sustainable communities are communities where the people living there pursue sustainable life styles and they pursue these life styles together supporting each other.
There are some parts of a high density, sustainable community which requires centralization in order to be economically viable and sustainable. While high density and sustainable don't seem to go together, people are migrating from rural, low density communities to urban, high density communities all over the world. See URBANIZATION AND THE MASS MOVEMENT OF PEOPLE TO CITIES and Migration and Its Impact on Cities
See What drives cities to pursue sustainability policies? and the postings in World Bank blogs - Sustainable Cities as well as Pursuing Sustainable Communities: Looking Back, Looking Forward.