I guess I should finally make this official: I won't continue developing JSFML.
This is difficult for me on one hand, but on the other hand it will make my life easier and make things clear for people wondering what is going on here.
To answer the latter - nothing is going on with JSFML from my side. I am packed with work - producing music, running a small music label, studying and working at the university - and last but certainly not least, there's life itself. I have not been using Java in almost a year now, because my job changed and I grew to hate Oracle's BS. There is no development environment for JSFML that I maintained. Building the native stuff for multiple environments has been a major pain, because I have no frequent Linux system nor a Mac. To make things worse, apparently, SFML cannot be built on Windows 10 / VS 2015 without additional efforts - so my Windows environment is nixed for SFML as well.
Each time I try to motivate myself to get JSFML updated, I hit on issues like this and it plagues me. I have no use for it myself anymore and thus, I decided to just drop the burden now. Everything is on Github, so whoever wants to pick up on it: please go ahead! I'll be available to answer questions about how it works.
I apologize to those who rely on JSFML and were hoping for timely updates. Thank you for your interest in the project!