Sketch assistants were a good idea, but I think the technology wasn’t available at the time to make them truly useful. They could basically list out areas of your design that had issues, but wouldn’t actually do anything about it for you.
Now that AI is out there it seems like the perfect thing to combine with assistants. I know I’ve seen Emanuel mention that they are really considering a good / ethical way of using AI. This seems like a good place to start to bring back assistants from the dead.
I agree with you, the idea of assistants for Sketch was really promising, but the technology at that time did not allow them to be truly useful. Simply pointing out problems is not enough, it is important that the assistant can offer specific solutions or even automate corrections.
With the advent of AI, the situation is changing - now you can not only identify errors, but also give recommendations, generate edit options or even create new design elements. The main thing, as Emanuel correctly noted, is to do this ethically and with respect for the work of designers.
If we can find a balance between automation and user control, such assistants can really be revived and become an important tool in the work of designers. This is a very interesting direction of development.