I would really like to use Julia as a "Matlab or Octave but with nice string concatenation" but the UI is just lacking for one off calculations and data processing.
Matlab have quite good such capabilities, Octave is more limited (you can't add titles, labels, regression lines or brush away data points, get simple data statistics like sums or std devs like in Matlab, but you can zoom and pan, save to file etc).
Julia seems to launch a Qt-window with plot, so adding some menu bar with zoom and pan shouldn't add too much bloat.
E.g. exploring roots benefits from zooming a lot.
EDIT:
You seem to be able to switch "backend" of Plots to eg. PyPlot for some functionality I didn't know that.
I agree that there's room for improvement here, but I also think that it won't happen in Plots.jl (and if it does, it'll depend on a backend that already provides interactivity). I think it'll be more likely to see something like this plop out of Makie.jl or something built on top of Makie.jl, as that has a lot of primitves for interactivity available already.
I used to deliver project reports to customers using a combination of Julia and LaTeX. It was perfectly suitable for that application.
You could use Julia to build some kind of GUI plot-making tool.
As a heavy octave user, I never felt a need to concatenate strings in any way. But I'd be happy if julia was an Octave but with fast loops, which it sort of is; but still not really there.
But ye for normal use it is not really a problem.