Thought process on this? If a person needs to dip into their retirement plan because a start up fails then they would be penalized, if that's the situation it's better to just keep it in cash.
Employees should always contribute to a their 401k at least up to the company match, as it is essentially free money.
Some IRA companies will let you do put it into a traditional IRA then do a Roth conversion, but then again some will make you mail them a notarized form every time you want to do that.