The Next version will be version 2.0, and is going to be a significant change across the board. So it will be a separate purchase, but I expect to have an upgrade pricing for those who have version 1.0.
At least, that's the current plan. Other alternatives include to enhance the core to allow different targets to be addons, and make those addons available to purchase.
Anyone pledging one of the tiers that includes a Kwyll license will of course get a 2.0/Next license.