All have fallen very short IMO. Coursera's courses are generally pretty watered down compared to the real undergraduate versions with a few exceptions here and there. Udemy focuses more on skill-based courses and they also have a huge issue with enforcing copyright. A lot of people are uploading pirated materials to the site and masking it as their own creation. The courses aren't that high quality compared to a traditional university setting. As with coursera, there are a few exceptions but overall most courses are low quality.

Khan academy is more for short tutorials where you need help here and there. It does play a role though but I don't think it is anywhere near possible to replacing traditional university education.

I think most people would agree that they want to see some sort of online learning system that can actually compete with a traditional university. As in, if I want to take physics 101 I can take it either at a traditional university or this online university. The online university would offer cheap/free and high quality courses such that you would basically be learning the same thing as the traditional course. It would also be possible to have a better overall learning experience thanks to internet/computer enhanced features (simulations, interactive videos etc.). Ultimately it would have some sort of certification, verification system that employers would place value upon, similar to the value currently being placed on BA degrees.