Probably one of the toughest part of maintaining GopherJS is that you have to run pretty fast just to stay in one place... There is a new Go release every 6 months and if it includes new language features, we have to find a way to support them. And only then we may have a bit of time to improve on the project itself, which is kind of stressful.
For the past 4 month I've been plugging away on generics support and I think there's only one major unimplemented feature. And a fair amount of bugs to fix. And by the time I'm done, adding Go 1.19 and 1.20 support will be due...