I know that I'm taking a position that is inherently unpopular and counterintuitive, but please hear me out.
If one of the skills that one needs to truly do martial arts (or any other) is the understanding of how the move works, where it fails, and what are the key aspects that lead to success or failure. This is why years of experience in a teacher matters. Instructors learn by seeing so many students fail in so many ways that the instructor would not have ever thought of failing. Seeing it done wrong, or at least differently, and in so many ways gives an instructor insight that they would have not had if they were only ever a student. This understanding then provides feedback to the teacher and clarifies the technique in the teacher. Almost every teacher says the same thing – teaching improves your basic skills.
Along with teaching, this self-awareness of technique can be gained by focused observing of others. Not just mindless hours watching kung fu movies (not that there is anything wrong with that, just not helpful for this possibility), but studying of various ways that various people teach and execute the same method. The ability to compare and contrast teachers, techniques, and styles is a well-established means to gain proficiency. What has changed is the breadth and scope that of what one can compare with current technology. Is video comparison as good as actually teaching a class? It could be, and if done right, this video comparison could be better than teaching.
So, if one could gain the insight of a teacher, could one develop the proprioception necessary to execute the moves without outside expert feedback? I don’t see why not. There are many tools traditionally used that are designed to provide feedback without the instructor. A wing chun dummy or even a simple speed bag both provide technique feedback without an instructor. Adding in now the ability to actually see oneself via video, one could get the necessary feedback, combined with a “teachers eye” to bootstrap oneself up to a skilled martial artist.
Considering that the library of necessary images is only now being built, it is easy to say that since no one has learned fully by self-instruction, it must be impossible. But, out there is a kid who learned math, language, and art via computer video lessons. Is martial arts really that different? I would say not, it presents a set of challenges, but there is nothing in this physical activity that prevents deep understanding via a video learning based process.