While I can understand that for basic stuff, there is no way I would ever attend an online course on some advanced undergraduate topics in physics or mathematics online.
There is a benefit of being in a classroom environment when learning an advanced subject. You have a direct connection to the professor and other students, which is essential for advanced material. Plus you can easily go and talk to them afterwards for more details. I learnt a lot by going to professors office hours which doesn't work online.
Also, what about labs? Every science program I am aware of has a laboratory component. That cannot be done at home. Plus good luck trying to get universities to agree on what labs to do. Each university has different types of researchers who focus on certain areas, which is reflected in the labs selected. My former university, for example, had no particle physics people so any lab related to particle physics would be misplaced. Instead they had a lot of quantum people so the labs were more geared towards that. I know of another university that had a lot of particle physics people and their labs reflected this.
Another thought is research. How would undergraduates get exposed to research in your system?
Thinking about it more, having TA'd first year calculus, you need to be able to interact in real time with students. I think online resources are great and I recommended them to my students, but they cannot replace face to face interaction. This is something online technologies cannot replicate, so I say it is a bad idea to even do it for basic things like calculus, which is very fundamental to the sciences.
Personally, I think it is a noble goal, but unlikely. Instead, I think the universities should integrate online stuff in addition to in classroom lectures.
EDIT: I forgot to mention the university environment. Being surrounded by my peers in the same field really helped. I learnt a lot just by hanging around the various clubs. That absolutely cannot be replicated online.