Maybe a trade system ( like auction house ) for your solo island. If you dont have stuff u can get it on auction house.
To be more clear, this is used so players can sell/buy things from each other. This would mostly be used for your own island but the auction house itself could be in the skyblock hub for players to access.This should be detailed and used for the Skyblock hub and not only for your island... Explain how does the system work and where most likely and how often to use it... I can't give my opinion unless it's detailed :/
Trading is an extremely sensitive topic. Now I'm not sure if you've noticed, but our economy and Skyblock is rather different to other Skyblocks. We're solid when it comes to progression from one thing to another. Now if I've just joined Skyblock, get some coins and I can get iron ingots, that will ruin the rest of the Skyblock experience for me, because I've gotten access to something that I should get 6 islands and 100+ quests later.
I'm not saying that Trading will never happen. But it will be extremely restricted if it was to exist. Such as you cannot buy or sell a specific item until you completed past a specific quest to avoid you getting an item or block you shouldn't have yet.