Would a petition change anything? Maybe just writing them and suggesting they add Lisk wilĺ go a long way. Coinbase is a private company and can do as they like.
It will change everythink. Of course you can write to Coinbase and tell them "Please add Lisk". But what they do in you are alone ? This pettition have to show our power- power of Lisk community, we have to show them that this community is really big and still grow !