It's hard to say what could be constructed as much has not been tried. Although of course tribal society was successful for a far longer period of time, I mean humanity has been tribal for a longer period of time (than it has existed otherwise at present, and than it may continue to exist without nuclear weapons and environmental destruction ending the whole thing perhaps). To say whatever is currently is, is successful, well of course it's a "might makes right" argument, but you could argue the same thing about any period of time, the Middle Ages, the Roman empire (lasted far longer than the U.S. is likely to), the centuries this piece of land was home to native Americans. Until they weren't. And they all seem to have lasted longer than this is going to, but that's a prediction that can only be known with certainty in hindsight (if there's anything left alive with the consciousness to know), but the trends aren't good, and this period of time is short yet compared to most others.

I'm not that keen on the capitalist label. My preferred term is "the existing economic system". Although I mostly prefer that because what someone has in their head when you say capitalism depends on who you talk to and I don't want a concrete point I'm making about this economic system, diverted into endless theoretical alleys.

The current system is unchecked, increasingly unchecked as far as protecting anything but profit, as far as protecting human (or animal) life, health etc.. But it's not without state support of course. In fact it absolutely depends on it. What the economic system would look like if no bailouts had happened I can't say. But it wouldn't be smoothly the same exact thing. Without trillions of dollar in bailouts it would be different, I don't comment on whether that would be a better or worse difference (except when your economic system seems to aim only for the extinction of life on earth, everything starts to seem a chance at something better), and it may have sparked revolutions or evolution or mere collapse. What it would look like without the U.S. empire I can't say but it wouldn't be this, some forms of capitalism may or may not exist without the U.S. empire. And some argue capitalism could exist with protectionism, in fact more protectionist periods have been called capitalist, but that would be a less out of control form if it did, since national governments could regulate national common welfare if they wanted (that's not the world of the TPP). It strikes me as a more workable form in terms of being democratically accountable. But the existing and unfolding economic system (some call it neoliberalism), is an out of control unmitigated disaster.

But unchecked-capitalist-consumerist-free-market-imperialist-democratic (as opposed to socialist) society seems a bit unwieldy.
Democracy what's that? Ok I'm not just going to argue the U.S. isn't democratic, that may very well be, but I want to argue there are forms of political democracy. There is direct democracy and there is representative democracy, the results might be different. There is democracy where politicians are chosen out of the population by lottery (lots) rather than being the same old representatives (if we have a jury of our peers why not a government of our peers?). That too is a form of representative democracy. Within even the existing form of having designated representatives there are voting schemes. Consider a voting scheme like this at the most simple:
http://scorevoting.net/Approval.html

Is it any less democratic than what we call democracy? (and it's representative democracy as well). I don't see it. Would it lead to very different results? Would Nader have been President? Ha, now I doubt we know that, but overall such a system would likely lead to some different results. There is also representative democracy where we actually had some immediate power to hold our representatives accountable (democracy with recall power like some states have where we could immediately push recalls of these TPP signers - not sit around and twiddle our thumbs until the next election).

Most things are untried. I fundamentally don't believe in an ideal society constructed in a test tube, but most stuff is only minimally tried in the real world. Most forms of democracy are untried. Most socialist projects are untried. I'm not talking about the USSR, it may have been a corruption of the original intent, but that corruption was tried. I'm talking: the U.S. government has crushed most attempts at leftist government (even anarchists movements) since then worldwide, with straight out coups at times, with mass murder when necessary, even putting in brutal right wing dictators (you could argue the left wing dictators are no better, but you can't argue the coups didn't happen and abort what would otherwise have happened). If "might makes right" this hardly matters but .... it matters if you are arguing what is and is not successful when not crushed by outside force.

What's the point of thinking about something like approval voting in the link above, when it will never happen anyway? It's just some kind of esoteric math exercise for geeks right? Well it's a thought experiment. To show that there's no such thing as one form of political democracy. But also why won't it or countless other things ever happen? Why do we continue to pursue an obviously failed system to extinction? Just sheer stupidity and thick-headedness, a failure of imagination? Because it never was accountable to most people anyway, and we have no power to change it short of revolution anyway and we'll be shot in the streets for trying, the iron fist behind the invisible hand, while the elite are completely out of touch with reality and morality? Because we personally have divine favor that we as individuals and a species will be ok no mater what happens? I think we have no such thing! Because there are no easy fixes? Yes, but I don't think it really explains the lack of even trying.