It's a bit of a chicken and egg problem. Really the argument is the problems with dual-language model will never go away, so Python & R face an ongoing cost disadvantage in the long run. However, they are also much more mature.
So assuming previous assertion is correct, you need to get enough people interested in Julia to grow to the tipping point.
I'm not really sure it will work, but can see the argument. After all technically superior platforms for this existed when python got started (heck, early python was next to useless for data work beyond file parsing) but that didn't dissuade it's use. The non-technical arguments made it a good-enough language and once that had momentum it's compelling.
On the third hand, what julia really needs to attract right now is mostly library/package writers - that's a tiny fraction of the users of python, but basically steers "what's next". However, for library writers, how many people might use it can be a deciding factor on investing the time...