Affinity Designer has found an interesting solution for this. I haven't done any complex illustrations with lots of brush strokes yet, it's just important that the performance doesn't suffer with lots of brush strokes (as with complex vector brushes).

Some years back, Adobe introduced Image brushes to Illustrator. The implementation was uncharacteristically shallow for Adobe who usually adds plenty of functionality and flexibility to any tool, which is great. Well, the images brushes were introduced, and I suppose abandoned and never looked at again. I think Adobe needs to revisit image brushes and add a lot more functionality. The best image brush implementation I've found so far in any software was in Serif's discontinued software called DrawPlus. That's what Adobe needs to shoot for, at least. Think about this. There are true vector brushes in Illustrator that are so complex and heavy that they are completely unusable. I've taken some of those brushes and converted them to DrawPlus image brushes where they perform great because they're only images that look like the original vector brush. So one advantage of the image brush is that it can perform well where a complex vector brush can not. Also in DrawPlus, you have the ability to add color which is not possible in Illustrator. Another big advantage is the kind of shading that Serif's newer program called Affinity Designer is known for. Again, Illustrator has pure vector shading brushes that are completely unuseable because of how poorly they perform. The image brush can do wonderful shading. The system is already in place in Illustrator but the high performance brush is what's missing. This would add something awesome to Illustrator. There was one other program that had brushes like that. Microsoft's Expression Design, also discontinued, which was built on top of a different, earlier program that was also discontinued! Now there's Affinity Designer that just doesn't get it right. I'm hoping Illustrator will revisit this tool and workflow and make it into the tool that it should be. Right now, images brushes in Illustrator are just pitiful. You can't even do something very basic like coloring the brush stroke.

It would be awesome to add pixel brushes in Illustrator as well as an easy way to paint inside objects, it's really not a ideal workflow to jump to Photoshop and even working with Affter Effects to keep those textures. Maybe something like Astute's Texturino or Affinity Designer's pixel layer.