Why did this never take off?

[Trass3r]

Any blockers? I only found these information talking about performance: https://wiki.qt.io/Qt_Contributors_Summit_2019_-_moc_and_QMetaObject
Especially the clang plugin seems to be a great approach.

[arBmind]

I guess the biggest downside is, that moc-ng clang plugin only works with clang. Also you have to compile the plugin for your local clang installation, which might not be under your control.