I did not consider it a gamble, rather an opportunity to teach something that is valuable to the students. It is my impression that many of the students kept on using Julia after the course, despite, of course, constantly grumbling about plots and the constant need to restart the kernel (this was before #265 was fixed). But this situation may be special to economics, where some prominent people are promoting Julia.
Interact.jl allowed us to program some “experiments” about numerical methods, allowing students to explore various options visually. I think they found that pretty impressive (I know I did, it was very easy to set up). So even half a year ago I would not have complained about plots, it was an effective teaching tool. Back then we had to restart all the time because of #265, which, combined with the slow loading, was really painful (insert favourite Four Yorkshiremen reference here).
The single reason that makes me hesitate to push Julia universally at the moment is not plots, but the “dataframes” ecosystem. My impressions is that something very nice will eventually evolve, once named tuples are in and the interface stabilizes, but in the meantime large changes should be expected, and anything specific I would teach today would be obsolete very quickly.