I think it's important not evaluate the limitations in relation to the limitations of individuals. If you want to collect the various filaments that are compatible with 3d printers, it's rather simple. Most all of them are readily available and they are rather inexpensive. While one person might say that $75 for a roll of filament is expensive, another will say that it's inexpensive because out of the roll you can print hundreds of items, making each one $.075 each.

Certainly someone with an extremely limited budget may have trouble affording 8 different filaments at $40-$75 per roll, but that's not 3d printing's fault. 3d printing has been exceeding liberating. As with any technology, you need to understand what it can and cannot do and need to compare apples to apples. If you understand that 3d printers need a flat spot so you can stick it to a print plate and you understand what happens with overhangs and you work to design objects that take that in mind, 3d printing as a process has very few limitations.

I'm an Industrial Designer and prior to 3d printing, the only way to get a design prototype model was to hire a model maker to build your prototype, usually upwards of thousands of dollars. Now you can create that same prototype for mere dollars or cents. That's not a limitation, that a revolution.

And if you want to go bigger, there really are few limitations. As long as you are willing to keep expanding the x, y and z hardware so that the hot end can travel farther and farther, there really aren't any realistic limitations. Sure, on a limited budget someone may not be able to afford that. But the question is not about budgets but about the technology.

3d printing has exponentially more advantages than limitations when compared to what we had to do before to achieve the same end product. There will always be someone who has trouble affording a $20 cheeseburger. That does not mean there is anything wrong with cheeseburgers.