In test games I've been able to get the policy without much effort by the end of the Medieval era, which isn't particularly late. It's about when TPs get their river bonus too. This brings them up to 3

tiles. Combined with the cost-reduction policies earlier in the tree I think it's probably worth it, though it requires more playtesting to be sure, which is what the beta is for.
Based on feedback, I've been considering possible ways to mix up naval-empire bonuses more with the other policies in the Commerce tree. This iteration is my starting point.