I disagree that it couldn’t come out of thinking of how to justify merging spacex and Tesla which he’s wanted to do for a long time.
This isn’t a cool car, it’s a gimmick. It will never be road-worthy, would lose money, and I doubt they’ll ever even sell it to customers.
As to why he’s going this dog and pony show now, we can only speculate, but I can’t think of any reasons that are good for Tesla (vs Musk personally) can you?