I mean, yes it would be pretty cool if there was a trading system actually. Don't know how they'll ever get that in the game but I assume the developers are smart enough to find out how. I wouldn't let everything be sellable tho, like maybe spawners but stuff like sappelings and stuff not. It's because people who aren't that far in the game would get a boost you know?
Maybe move your suggestion to the threads under 'Suggestions' or 'Skyblock'. :)