Mark H. Harris
At this point in the discussion please try not to think "implementation," rather think conceptually in an open framework where anything is possible.
As I understand, you are suggesting some kind of number system with symbolic representations that can be converted to decimal if needed. The topic is so vast that the only chance of it happening is for someone to provide an implementation on PyPI and see if people like it. There are packages for symbolic mathematics like sympy, perhaps that is a start. Even if people like it, it would be nearly impossible to integrate it into the core language without breaking third-party packages on a very large scale. So it is unlikely that such a thing will make it into the (hypothetical) 4.0. Regarding decimal literals: Possible in 3.x, but it would require some investigation if people really want arbitrary precision arithmetic by default rather than e.g. IEEE Decimal64. Regarding decimal floats by default: Perhaps in 4.0, but IMO only with *full* backing by the large SciPy and NumPy communities. My guess is that it's not going to happen, not in the least because the literature for floating point algorithms (with proofs!) has an overwhelming focus on binary floating point.