But without a default tariff it would not make much of a difference it would almost feel like u just got embargoed which is rarely used
But with a default tariff u would have to get some sharedmarket with ur allies or if u are a member of an alliance u would have to contact specific suppliers to import stuff to your nation which might be a bit annoying but would make politics and war a bit more active and intresting
I think it would be awesome if u could set a default tariff to all alliances making it a lot more useful to trade in the sharedmarkets also i like the idea that alliances could sanction bad alliances with it without fully blocking the trade with them