If a startup never finds any paying customers, it will never IPO. The IPO is a separate step from the initial investment, governed by rules intended to protect the public. ICOs don't seem to represent anything of intrinsic value (e.g. a successful business) so the public probably faces greater danger from unscrupulous behavior.
In the biotech / pharma world, it's common for startups to IPO years before they have a single paying customer.
The difference between a biotech startup and many ICOs is that the former typically has years of validated and peer-reviewed scientific research backing up the hope of eventually having a product.
In that case, the "customers" are other scientists and drug companies that _consume_ the research, will pay for partnerships, will pay for research to be done by that lab, etc.. ICOs on the other hand don't have an acclaimed lab or anything special other than a PDF with some buzz-bullshit.
