Ask HN: If you had 5 years of uninterrupted time, what would you build and why?

Everyone seems to be busy building MVPs in a weekend or in few months of time, and thats great as new technologies allow us to build much faster than even 10 years ago. But I want to know with that mentality and short time spans, what kind of stuff we avoid building simply because it would take years to make and has high opportunity costs for a single developer.

So as a hacker or an entrepreneur what product would you create if you have 5 years of time if you were sure you can not fail ? to put differently, What are the tough problems you think we need to solve but you simply don't have that much time or resources to do it? a new Mobile OS? file system? new language? what could it be?

EDIT: From the many comments, its interesting to note that some of the ideas are borderline science fiction! Amazing to know what a mere 5 year timescale allow human mind to think up.