Given Julia has macros, so it will definitely catch up to R and data.table in terms of syntax (if it's not already there). I am more thinking about performance, e.g see
https://h2oai.github.io/db-benchmark/. It shows that Julia is lagging behind on group-by (and from my experience many other operations) when compared to R's data.table.
Although I have done some work to make thing fast see: https://github.com/xiaodaigh/FastGroupBy.jl. I have yet to update it to Julia v1. Hopefully, I will get to that soon. However, the improvement I have made only works for grouping up to 2 group-by variables and I need to learn more about generated functions to make the code more generic. So from my (someone who's actually spent time trying to optimise these data operations) perspective, Julia will take a while to catch up. Hats off to the data.table crew!