Once a stock has at least 2,000 acredited shareholders or 500 unacredited shareholders (was 500 shareholders without regard to acreditation before the 2012 Jobs Act), SEC disclosure requirements apply the same as if had IPOd. Allowing/encouraging trading of the stock is going accelerate the time that that happens. Facebook aproaching the shareholder limit was one of the things that pushed them to IPO --- might as well raise some money if you have to prepare all the disclosures and follow all the accounting rules, anyway.
