It's easy to unban your 3DS if you get banned. I wouldn't worry too much about it.If I really wanted to homebrew my 3DS I would just buy a gold card separately for it in the future which probs will not happen until the DS is not supported anymore, plus I really care about 3DS multiplayer and too scared of bans
btw I did not pay for it yet tho
EDIT: I did heard they are working on a exploit for R4iSDHC Dual Core so...