If Elon launches his own crypto or gets involved with a cryptocurrency project, it doesn't necessarily mean that the project will do good or bad, the only thing that will worry me is that too many people will take his public opinions (tweets) as a signal to either buy or to sell the cryptos and that is not healthy for any business.
A good crypto project should have what it takes to withstand a FUD or shilling by its project members
Given the gigantic following he already has, he would definitely have less of a problem to get a relatively big community unite behind that sort of a project. However, he already said he wants to give Dogecoin a try and he sounded serious about it. Nobody knows whether he comes forward with a real plan or whether he is still just trolling and making fun of people.