So, since there is no qualifying event, investors could get stuck without any ownership for a while. for YC this is most likely a non-issue, but most other investors won't be able to, thus providing YC with a bit of extra edge in attracting great entrepreneurs. Fair assessment ?
A company that never has one of the qualifying events is likely to be an extreme corner case. So an investor could end up holding a safe for a while, but for the vast majority of companies, there will be a financing or a merger / acquisition at some (or an IPO).