Here's a thought:

Suppose that I came up with a really awesome program. I really want to keep the source code myself, but I'm willing to sell it to others...

...except I'd developed it in singleplayer.

What I'd like to see is a sort of "quantum floppy" - one whose contents are saved on an official Mojang server or something, linked to a username. For balancing (and RL Cost) reasons, each player only has one such space on the server.)

Storing these "quantum floppies" wouldn't be too costly for Mojang - 1 GiB of HDD space could hold up to 728 users' 1440 KiB QF's, which means (after a quick Google search and picking the first item - a 1TB HDD for $183) that it's roughly 0.03 US Cents per user's QF.

And if you're asking for data out of the QF sector-by-sector, that's roughly 1 KiB of data (1024 8-bit bytes) being sent through the network. Taking the supposed 2009 Internet speed average for the United States at around 4.8mbps, or 4.8 megabits per second (no matter how potentially unreliable that source might be), that's roughly 1.71 milliseconds per sector... which, according to the M35FD specs, quoting a read/write speed of 30.7 kilowords per second, or 61.4 kilobytes per second, or 0.4912 megabits per second, there's plenty of time for this data to come through a halfway-decent Internet connection of 2013.

Calculations (and Wolfram|Alpha) aside, there's one huge use I could see for a Quantum Floppy. Yes, granted, information could be transferred between saves / servers / dimensions / whatever we're gonna call it, but I can definitely see that there could be a number of servers popping up, with the sole purpose of trading code between players. There could be a whole economy (and a potentially huge pirating community) based around code trade. Alternatively, it could be used to allow players to go on various servers with their favorite programs in tow.

Again, yes, this is all subject to whether or not Mojang will allow this, but, hey, you never know.