There’s no real world brokers or workers supported (at least built in), but still centralising around a standard interface might make things nicer than the celery tentacle monsters Django apps eventually tend to mutate into.
Celery is large and complex now and edge cases always show up at scale but that is usually not a reflection of the platform quality. The custom implementations I've seen are no where near what celery is capable of and can cater to so haven't seen the edge cases yet but that doesn't mean they implemented bug-free code and celery hasn't.
After asking about it, the issue always went towards a hand-wavey "performance". What is your experience on that front?
I never considered writing my own, I just want a tool to plug in and work so I can focus on the application. I also never thought performance of this part of the stack would be a bottleneck for my use cases.
In contrast, I am happy to use Django over Flask because you can't get away from needing lots of web framework features for a nontrivial web app. The bigger framework is usually justified, especially if it's high quality like Django. But spawning tasks (for my use cases) is just an aspect of the project that can have a simple interface and it doesn't justify adopting a big framework. Time I've invested in Django (going back to 2009) is still paying off for me today, but there'd be much lower ROI on the time I'd have to put into Celery. Unless my projects really needed its complexity, but I think far fewer projects actually require that in practice than their architects tend to think.