You'd still need to solve the double-spend problem, because while contract state on Freenet will usually synchronize within a few seconds, it isn't guaranteed to converge to a single globally consistent state.

Freenet's approach works well for things like group chat, where temporary inconsistency is mostly just an irritation, but for a cryptocurrency it is fatal.

I'm not saying you couldn't build a cryptocurrency on Freenet, but you'd still need a solution to that problem.