First suggestion has been suggested several times, don't really see that happening as it is not super rare to get barrows drops (even with row(i)). Duplicates can suck, but I don't feel we need another minigame that shares the same system as Mage Arena.
As for your second suggestion, I have seen similar suggestions regarding kicking out inactive members of your team. 48 hours is too short, in my opinion.
Overall, I am supporting neither of your suggestions. For the latter suggestion, hopefully Omicron can figure out some sort of system to kick/leave from groups than cannot be abused.