This will never happen I fear. And IMO it's not even a matter of interface issues -- environment, language, etc. -- although matching those would take a lot of effort as well.
But more importantly, I think a lot of people massively under-estimate the sheer number of best-in-class implementations of important algorithms that are locked up in Mathematica's source code. I try to avoid Mathematica whenever an alternative exists, but in a lot of cases there just isn't an alternative. Especially as you get closer to "real" mathematical capabilities.