There is one more advantage: You would have a very small blockchain at the beginning. Bitcoin "beginners" wouldn't have to download 107 GB and that would be a competitive advantage.

But the reason why I would like to see a "BU altcoin" is that it would be a way to test it thoroughly "in the wild". As many Core supporters (including me) have doubts that its consensus will work as expected, it would be the opportunity to the BU team to show that it works well. In this case it's even possible that at the end Core adopts it and the "original BTC" would come with BU rules.