Under uClinux, executables can be position independent or not. They can run from flash or RAM. They can be compressed (if they run in RAM). Shared libraries are supported on some platforms. All in all it's a really good environment and the vfork() limitation generally isn't too bad.
I spent close to ten years working closely with uClinux (a long time ago). I implemented the shared library support for the m68k. Last I looked, gcc still included my additions for this. This allowed execute in place for both executables and shared libraries -- a real space saver. Another guy on the team managed to squeeze the Linux kernel, a reasonable user space and a full IP/SEC implementation into a unit with 1Mb of flash and 4Mb of RAM which was pretty amazing at the time (we didn't think it was even possible). Better still, from power on to login prompt was well under two seconds.
You are correct in that the decNumber library doesn't support trig operations. Arithmetic, log, exp and square root plus rounding and some conversion functions.
My experience is that decNumber is generally slow. Logarithms are especially slow. Intel's decimal library is much faster & as you noted, it uses binary operations to start it's algorithms.
Cost to orbit is huge. Power availability will depend on pushing enough solar up there. Data centres use lots of power.
Getting rid of excess heat is a major problem in space and data centres generate lots of it. Terrestrial cooling is trivial in comparison.
Hardware obsolesce will be a major hurdle as will repairing stuff that fails.
Radiation is a significant problem in space. Shielding will be very heavy or the hardware will have to be build tolerant which is much more expensive and results in a much slower solution.
Much easier and cheaper to install lots of solar and batteries in the middle of a sunny desert somewhere really cheap and build your data centre there. Then build fibre connections to wherever.
This is the easiest way to go but it's only obscuring the GUID.
Format preserving encryption (FPE) would be another possibility if it's not simply a byte string.