Libre Arts has posted an
interview with four Inkscape developers.
From what I understand, what helped was finally porting the user
interface from GTK2 to GTK3. It was just a huge task and brought
many regressions, some of them are still in even after 2
years. Just to compare, 1.0 was in alpha state for 1.5 years; but
for 1.1, it was just 3 months. So if you want a faster release,
don’t port your app. Too late for us though! And we probably need
to port again to GTK4 now if we want to fix performance
regressions.