That will never happen, and it won't happen for the same reason why we have social safety nets in the first place: we're too nice to let people who can't handle money suffer. As soon as someone lets their kid starve because they blew all their money on drugs or at the casino, food stamps will be re-invented.

A necessary attribute of a "safety net" is that it be as fool-proof and fail-safe as possible. Just giving someone money to spend as they wish is neither of those things.