Sustainability
The basis of this project wasn't to come up with something that would necessarily be a better economic model for the environment - not that this isn't an excellent goal or a critical aim to pursue, but simply because the scope of the project, while ambitious, still had limits. However, as I have worked my way through the implications of reshaping the economy, one happy result is that there is an inherent move toward greater sustainability in a giftmoot economy. Most of this I have already been over in one manner or another, but I think it is worth summarising it here just to cement the point.
Better business practices
I've spoken about this more than once, but a giftmoot economy - where work is volunteering and can be safely quit at any time, and where businesses aren't motivated by profit - are likely to have more socially beneficial business practices. Businesses would not be motivated to make things that break easily, or that have planned obsolescence, or that people don't really need but which they want to convince them to buy anyway. Businesses would not need to construct demand to sell more things. Businesses would be more likely to only make things that people need, to make things that last. Each of these factors would reduce the load on the environment, because it would generally mean making less things less quickly.
In addition, businesses are far more likely to make things in a manner that is more sustainable overall, with less pollution and out of less hazardous or environmentally exploitative materials. Businesses don't need to save money, and they don't need to make money, so instead of weighing up potential profits against production costs, they would weigh up different types of production costs - for example, time versus the environment.
No indefinite growth
Exchange economies have a paradox of efficiency, where labour efficiencies exist in tension with labour survival. But they also imply something else: every time there is a labour efficiency, we need to create more jobs to offset it. This means that the rate of production of things generally has to go up, as the rate was maintained when the efficiency was implemented, and we have to add the new jobs to account for the displaced workers. The conclusion is indefinite growth: the economy needs to keep growing and growing to offset all of the efficiencies that are created.
A giftmoot economy does not have the paradox of efficiency. When there is a labour efficiency, one possible solution is that less people work while the same amount of things are produced. That means that, at the very least, production does not necessarily have to grow and can be sustained instead.