I wish that were possible, it would be a great thing. However, what you are describing is essentially a public offering, and the listed companies would be subject to all of the associated regulation (SOX included).

The loans would be legal however. This kind of sucks - I can loan 5K to a startup, but I can't become a shareholder. There has got to be a way to 'hack' around this.

How about a variable loan: one that would return the profits and/or sale of the startup as interest?

Why can't we call it a loan, but in the fine prints say that there is no guarantee to repay if the company goes bust. EDIT: And the loan is made to the Inc so if the companies fails, the owner credit will not be affected.

Well apparently the SEC is not going to like that.