Why do we celebrate holidays on the same day? If you're willing to celebrate Thanksgiving a few weeks earlier, you'll save on airfare, travel headaches, and inflated turkey prices. Or if you're willing to buy holiday presents after Christmas, you'll benefit from deep sale prices, while others pay full price so that they're able to celebrate on the "proper" day.
There's no inherent reason to celebrate on the same day as everyone else if you can coordinate celebrating with the people you care about. Maybe coordinated holidays push families to celebrate together when they ordinarily wouldn't. So the question is: would celebrating off cycle still feel like a holiday? Or would it feel like just another family gathering? It's all about mindset. If everyone agrees to treat it like a holiday, then for all intents and purposes it's a holiday.