The latest update is more than 6 years ago.
It looks quite abandoned though, so stabilising it at this stage is a bit questionable too. What is it required for, at all?
I had it for the GTK plugin, which makes Qt5 applications render using the GTK 2 theme. This was particularly handy when I used Xfce. I now use KDE, so I've stopped using it. With Qt6 coming and GTK 2 dying (including Xfce's usage), it's in need of a rework, although I imagine porting it to GTK 3/4 would not be trivial. I'm perfectly happy with stabilising it for now though. It always worked well and I never had any trouble with it.
Unable to check for sanity: > disallowed package spec (only = allowed): dev-qt/qtstyleplugins
amd64 done all arches done