Don't worry; the latest version of Eternity is compatible with the upcoming 0.19 Lemmy release.
As for the lack of updates lately, I am very busy at the moment with work/uni stuff. I might be able to spend some time on it during the winter break, but I can't guarantee anything.
Guys... is this your first open source software? This question comes up so much.
The people contributing to this are working for free, when they have time. They may not have time all the time. Sometimes it takes a few week before even a small addition is made.
The last update was October, the bigger one before that August.