Interesting idea indeed, even though I don't fully understand most of the technicalities regarding crypto currency, mining and block chains - it sounds like it could work.
The main difficultly , as I see it, in building eco villages isn't the cost of building ecological, off grid houses. It's fairly well known (at least in certain circles) that it doesn't necessarily cost much to build a habitable home. The problem is more one of rules and regulations.. (at least in the country where I live) .. you need to pay vast sums of money to get approval, planning permission etc, before building anything - which not only is expensive (and doubtful if the authorities would accept ecocoins for their bribes and signatures) , it's also hard to get permission at all for such building projects as they don't fall within accepted limits and regulations.