I think part of the reason that Mustachism works is because of the abundance created in the last 60 years. In certain fields, we are able to earn dramatically more than we could have in previous years. The cost of many products have dropped, allowing us to purchase even basic necessities for much cheaper.
I think that is a key point which he largely overlooked.
We ALREADY live in a world of abundance! The issues isn't lack of resources, it is distribution of those resources. Some people (the middle class and above in the first world) have already passed the point of diminishing returns from the value of additional wealth, while others are no better off today than they would have been with the wealth and technology available 200 years ago. The trend recently, even within our own wealthy country, has been for the people who have the most already to gain the most from the productivity technology produces (e.g. GDP rises while median wages don't)
Another thing he only briefly touches on is that population grows exponentially, just as technology does. Unless population levels off, then production has to grow as fast just to stay at the same level (per person). If food production per person doubles, but population also doubles, food doesn't get any cheaper or more accessible.
And lastly, our total rate of use of resources and energy goes
up with increases in technology, wealth, and accessibility. Despite - or more likely because of the increases in engine efficiency over the past few decades, we use more fuel now than before. Energy per computation has gone down for computers, but the total power draw from our collective computers has gone up.
The implication is that the benefits from technology will grow exponentially forever.
If a growing population uses an increasing amount of resources per person, then the question is "is it possible to have infinite growth on a finite planet?"
Maybe technology allows us to desalinate water cheaply, and transport it worldwide equally as cheap. There will always be some limiting factor. The aluminum example makes for a good story, but not all rare earth elements used in solar panels and computers happen to make up 8% of the Earths crust. If our use of electricity continues to expand at the rate it has, then the land area taken up by solar collectors will continue to be an issue. Just as people 1000 years ago could not have even imagined our technology, they could not have imagined our rate of resource use. And similarly, if we can not imagine what the tech of tomorrow will bring, we should assume our consumption will scale accordingly.
So, IF our (in the 1st world) level of consumption stays the same, then the tech blessings of tomorrow will allow the other 80% of humans to have the same comfortable live we do. But if the 99% of Americans (and Europeans and Japanese, etc) keep aspiring to live like the top 0.01% of Americans, then I expect the world to remain much as it is - at best.
In other words:
Mustacianism is the only true hope for the future of mankind