Subscription based screams a lot of greed from Bamco. They didn't want you to use the first switch game's DLC, but they also didn't want to skip having DLC all together. They knew a separate Song list with no compatibility wouldn't pass so they went this route. Pricing is pretty much the most important detail we don't know of.
Still, it's definitely a little sad that this will obviously be a Taiko with an expiration date.