I suppose working with mentors could help students be better prepared to join the workforce, but students can already do that on their own by getting internships.
Classes could be self-paced, but then likely many students would lose the motivation to learn. People are strongly driven by competition and deadlines, two things schools excel at providing.
There already are internationally recognized assessments -- standardized tests. Though they are typically useless without a degree. It would be difficult to change this, but if you could then you might make colleges obsolete. Many people would not spend 4 years and $50,000 on a college degree if they could study for 6 months, take a test, and get the same job. But I don't think this could work. For example, even though we already have the GMAT, GRE, and MCAT, it's unlikely you will ever convince medical schools to let in students with an MCAT and no undergraduate degree. And if an employer is choosing between someone with a perfect GMAT and no undergrad, and a Stanford graduate with a mediocre GMAT, the choice will likely be in favor of the Stanford grad. I don't think this would change even if you made the test more comprehensive and difficult.
Not being graded: this may increase students' intrinsic motivation to learn, but it also may decrease their motivation, since there would be no penalty for not learning the material. But if you maintain that students must take an internationally recognized test at the end, then test-taking abilities will still be measured, so you're just playing with motivation here and not really changing much.
These ideas are interesting, but even if schools enacted them, what great improvements would they bring to our society?