I thought the same thing as well. Unfortunately, there is still a bit of work to be done on the Julia side. The tidyverse ecosystem in R has relentlessly focused on ease of use and package compatibility, such that everything "fits" together in a logical way. I can't emphasize enough how much of a difference this makes in being productive with a language. Many of the things I do on a regular basis in R are actually rather mundane, and are possible to do in Julia. But it's just much more of a pleasure to do them in R.
Fortunately the DataFrames ecosystem and related packages (like Query.jl and StructuredQueries.jl) seem to be headed in the right direction.
Hadley, can you share a bit more about your plans for modelr and what need(s) the package will be designed to solve? Congrats on your book btw, I've been reading it for a few weeks and it's quite simply excellent.