@grant thoughts are like... everybody has 'em.
Julia doesn't seem to have captured the popular imagination yet. I suspect this is in large part because speed of computation is often relatively low on people's needs list.
I expect we'll see a {reticulate} for Julia and from the R side that'll serve most people's needs.
I think the next time I'm tempted to write C++ for speed in R or Python, I might give Julia another look.