Sure. That’s understandable. 3.8.15 is just the last time I checked and updated the readme.
The “compatible up to” is a bit misleading in this regard. All Menu Social Icons does is filter through menus and add classes for FontAwesome. The filters in use have been around and unchanged since 3.0. I wouldn’t expect it to stop working until the wp-admin Menu interface is completely abandoned for the one in the customizer.
Generally speaking, I’ve been unable to volunteer support or updates for my plugins on .org for over a year. Every plugin and every developer is different, but in my case, I wrote hundreds of thousands of lines of freely available code, and simply burnt out.
I wish I could offer more, or had a clear model for sustaining code on .org, but just like everyone else, I had to turn attention to systems that give back.
In short, most plugins on .org are volunteer, and in my opinion, most appropriate for users who can dig in and read through code themselves. If hands-on-support is desired, some of paid plugins on other markets may be a better fit.
Think of .org as a food bank, scrap yard, or library. If you’d like regular updates or customer service, markets offering a customer relationship are a more appropriate place to search.