2. Work at Google for a few years, start a 20% project
3. Leave Google, become a founder
4. Get funding, hire more employees
5. Launch a successful product, build a big userbase, get favorable media coverage
6. Get acquired by Google
The point of the 20% products for Google is to give the company startup-style flexibility. It works the other way, too - if you take a product from whiteboard doodling all the way to an official Google product, well, a startup is like that, except 100% of the time, on your own bank account, and with no admins/middle managers to take care of the business side for you.