I've used everything but Octave (sorry Stallman :[) and coming from a CS background, no other language/platform made me feel more at home than Julia.
The other huge reason for R adoption is it makes running stat analyses very simple, so for all the people who aren't programmers, and don't wish to be programmers, R is an awesome choice. The ability to, in 3 simple lines of R, load data from a csv, run a glm, and get a sophisticated report on the model is awesome.
I would be far more excited about the possibilities created by a cornucopia of new stats/dataviz functionality built into Python than I would be about some packages that make R a bit less terrible to write.
- JavaScript
- PHP
- C++
- ...
On that note, Hadley, R IS awesome and a large reason for that is your contribution to it! Thanks and keep up the good work!