The main advantage of a mirrorless camera is that AF for video is practical. Contrast detect AF is very slow for large sensors, but easy for very small ones as in camcorders. This is due to the huge depth of field and only a few lens focus positions.
We see lots of research and patents, but so far, nothing practical for a traditional DSLR. Thats why I'm not excited about DSLR video, I do not have the inclination to fool around with manual focus, even if I could see well enough to do it.
AF is of no importance to Movie makers, its not accurate enough. They have developed a system for manual focus and it gives them what they want. Thats why the HDDSLR is popular for budget film makers, low cost, high quality, and they can adapt cinema quality lenses if they need them, or use the relatively low cost Canon lenses, at least for 35mm and longer.
All this refinement is totally lost on me, I'll not be making any movies. My grandson, however, may indeed be filming movies, he is in college now and has written, directed, and filmed his work. I certainly encourage him and others to learn.