I worked for a company that was on the vanguard of trying to make ICOs legal and mainstream. Among other problems, there were tensions between trying to achieve regulatory compliance, transparency, and privacy of trades. I worked on a potential solution involving ring signatures, but it never made it into production.

There were some other important tensions too, happy to discuss if anyone wants to get into the weeds. FWIW I still would love to see a highly fluid market for shares in small businesses and pre-IPO startups.