The possibilities you list are interesting, yet I suggest you read another essay posted here about "legal/illegal" bitcoins, where governments could force one to "declare" what its bitcoin accounts are, and treat all incoming payments and outgoing payment to "undeclared" accounts as illegal, and tax accordingly.
This would the the perfect scheme to ensure orwellian control of the economy, with a complete history of the transactions. It is a possibility - that bitcoin is touted as a "libertarian dream" while it can be in fact used for complete control by the governement.
Today's currencies are too many and transferts not properly traceable. Make that one currency and add in the design that all transferts are to be logged, and it does not matter whether one uses a bitcoin address or its full identity.
With enough social network analysing and recouping information, especially with the governement weigth and files, it should not be hard to "uncover" the true id.
I find this possiblity interesting, even if far fetched.
EDIT: see the actual thread on https://news.ycombinator.com/item?id=5501803
Another possibility would be to reduce the "weight" of the financial sector. Having IIRC 10% of the GDP used for allocating resources is wasteful when there is technology available to do this very thing. I commented on Krugman article on https://news.ycombinator.com/item?id=5541189 along with additional details on https://news.ycombinator.com/item?id=5543308
Basically, using bitcoin instead of the current financial sector would remove frictions and transaction costs, improving efficiency. It is compatible with the standard economic approach, especially on grow theory, where growth is explained by technical change and human capital in many models - from the augmented Solow growth model to Romer and Lucas.
Bitcoin could then be seen as a way to "reallocate" the human capital "spent" in the financial sector to new productive endeavours - the lack of inflation being added to make sure that there would not remain any incentive to waste human capital on looking for ways to speculate.
That is the explanation I prefer at the moment - Bitcoin as an experiment created to improve efficiency of our economical system as a planetary level, by someone well versed in economy and computer science.
Yet out of your list of possible explanation, I would say (2) is the most likely. But if indeed it was government made, I would not say the US is the most likely author.
Look at how the european currencies tried and failed to replace the dollar as the world currency - sum up the Euro currencies place in world commerce before and after the Euro, and you'll see they failed. A bit like HP-Compaq merger, with total share of the market less than their initial shares.
This could support (3) and (4). It is also quite interesting to see how EU-wide directives about virtual currencies were implented and voted were created before BTC became very popular- see http://ec.europa.eu/internal_market/payments/emoney/
The second EU electronic money directive, 2009/110 dates from 2009. Considering how long the political process usually takes, I find having a directive voted and ready in its SECOND version in 2009, then implemented with only a year and a half delay in say France, "unusual". http://www.bryancave.com/files/Publication/515cae04-f1c0-46c...
The only thing that would not match this is how the ECB follows a Friedman like monetarist approach, with a 4.5% M3 monetary aggregate growth target, while bitcoin is not inflationary.
But when you consider the FED bad habits of "quantitative easing" (printing money), it make the US even less likely to be the originator.
TLDR : ranked from most likely IMHO:
1- it was created by someone familiar with economics and computer science to improve efficiency (compatible with the current analysis and the initial comment about central banks)
2- it was created by a public organisation, considering virtual currency inevitable, to make the most of them, but in that case, it is more likely from the EU than from the US
3- it was created by a public organisation, either aiming for, or having a side objective of, orwellian control.
EDIT2: about this 3rd option, I know the records list Trinity College as one of the potential "epicenters" based on published papers and software, but it does not excludes the possibility the effort was funded with this very goal in sight - give students money, incentive, ideals, and watch while they develop what you wanted.
Just like how BTC can be touted as a libertarian dream while it could also be very dangerous, initial creators could have been fooled by only knowing a part of the plan.
So I share pg opinion there. Some possibilites should not be discarded too quickly ; if it was possible to create STUXNET to harm Iran nuclear program, with all the complexity involved, and then keep the official involvement hidden for like 10 years, this gives a priory evidence that such a feat could be done as a government project.
I am quite concerned by this last "orwellian" option, as unlikely as it may be.
One of my side projects at the moment is examining this possibility - not shouting that too loud, because I don't want to be taken as a conspiracy theory nutcase :-)
Also, I only have an interest in economics - I'm not a professional economist, so there must be some flaws in my analysis.