I think the problem is that we don't have a clear roadmap -- if we did it would be much easier to execute on it.  In the limit, what Hall (and Drexler before him) describes is physically possible but transients matter and nobody has done a great job describing the intermediate technologies. 

Throat clearing aside, here are some of my personal hunches (I don't think there are any clear consensuses):

• Use a combination of our existing tools for manipulating matter with nanoscale precision to start building multi-component and approach nanoscale systems that we can interface with from the macroscale: lithography, DNA origami, proteins, molecular machines. [Dropping a placeholder to include a link to Drexlers paper from the 90s combining proteins and AFM tips, and Tuberfelds work on DNA origami 3D printers]
• Use these systems to at first start modifying macroscale objects: maybe making extremely precise edges to turbine blades, or something that can't be done any other way 
• Eventually expand to making things full cloth with them, with increasing scope and precision. 

There are so many big unsolved problems! Frankly I think the biggest ones are some combination of experiments taking a long time to do and then measure what happened and then trust those measurements, the difficulty of simulating what will happen in lieu of experiments, both of which lead to extreme difficulty building any sort of intuition for the affordances of nanoscale systems, which makes it hard for people to build systems. That's a rather abstract answer, but beyond "creating covalent bonds exactly where we want them" I'm not even sure we know what the right concrete unsolved problems are.

Two approaches I'm personally excited about: 

1. Using something like DNA origami to template nanoscale building blocks (that could be proteins or other things) -- you can get atomic precision on very small "pieces" and then if you can put those pieces together in a deterministic way, you could get larger pieces with the same precision. If you could then functionalize those pieces, you could very ambitiously have a nanoscale "factory" that does several steps of a reaction or something similar. (I am talking my own book to some extent here: we're running a program to tackle this approach at Spectech)
2. Interfacing silicon and proteins. Photolithography is great at going from ${10}^0$ m to ${10}^{-8}$ m and proteins are a great way of going from ${10}^{-10}$ to ${10}^{-8}$ m. By bridging the two we could potentially have something that enables you to directly interface with single atoms via a keyboard at scale. 

After a lot of research, I think that one of the most effective ways of allocating order one-$100M towards progress is to enable materials and manufacturing technology research that could shift paradigms but doesn't have a home in current institutions. Those conclusions come from a couple of observations:

• A ton of progress is driven by the second order effects of technologies: haber bosch, intended to remove german dependence on south american guano contributed a huge amount to solving overpopulation, etc.
• The technologies that most often have those second order effects are how we make things and the stuff we make those things from (ie. materials and manufacturing)
• These technologies require systems research, which in turn needs more coordination than academic incentives provide but is still too uncertain for startups.

Unsurprisingly, that's the strategy we're pursuing at Speculative Technologies.  

That being said, I'm not a fan of some sort of global prioritization of funding. While in practice everybody must make it, I think that the best thing for one person to spend towards might not be the same as for another person. 

I do think on the margin additional money towards startups or small projects (<$100k) isn't as helpful as pooling money together with other people to enable a discretely larger or longer project. That could take the form of giving one person ~10 years of guaranteed funding, enabling a team of ~5 people over two or three years, or building a serious piece of infrastructure for a group of weirdos. 

Not an expert, but as far as I can tell, nowhere near enough! There's some rumbling about making it easier to build nuclear and folks like Jamie Beard and Eli Dourado are doing admirable work to make it easier to drill geothermal, but for the most part people don't even think seriously about the counterfactual that we could have orders of magnitude more energy and what that would unlock. 

If by "investors" you mean venture capitalists, I'm not sure that material science will ever be as exciting as software -- the margins on software are too high and the timescales are so short. Maybe if someone cracked truly automated generative materials. 

But there are other kinds of investors -- I could imagine a number of valuable companies eventually being built around some general-purpose materials platforms: if someone figured out how to make steel with truly tunable properties, hierarchical materials, extremely efficient thermoelectrics, arbitrarily long carbon nanotubes, etc.

If you forced me begrudgingly to make generalizations about average people, I'd point to the fact that people get excited when advances touch their lives: you could imagine everything from drastically cheaper electricity from room temperature superconductors, self-cleaning surfaces, items made from wood with drastically different properties ... 

In no particular order (and for flexible definitions of "coming" and "soon" -- things always take longer than we expect and aren't inevitable): 

• Plastics made from atmospheric carbon (if Casey Handmer et al are right about cratering solar panel prices)
• I think? Varda is making fiber optic materials in space.
• The science things we can learn from messing around with graphene (not sure it will make a useful product anytime soon)
• (Maybe) Ceramic airplane engines

Not an expert but I suspect it's unlikely that commercial products will be manufactured in space beyond expensive novelty items (do theraputics count as commercial?) 

Reason being that commercial usually implies large scale, which I suspect will be limited in things in space that are going to come to earth.

Predicting the future is hard -- I hope I'm wrong!

I suspect that for situations where you want millions of the exact same thing, 3D printing will never replace high volume standardized manufacturing. 

However, you could imagine a world where additive manufacturing does become much cheaper and faster to the point where many more things are made with subtle customizations, or made on premise, etc. New paradigms almost never replace the old thing directly, but take over by changing the way things are done and measured.