This doesn't do much for caucuses, for example, and it sounds pretty expensive compared to the current system in some states. It's not just about party control of candidates or "gaming" whatever system is in place.

Many states require the local parties to pay for their own primaries. Many local parties are bare bones organisations that only ramp up activity every couple of years or so. Voting mechanisms need to be scalable, affordable across a diversity of budgets and technical skill sets. Caucuses, for example, exist because they are dead easy to explain, don't cost any money, and are transparent at least so far as everyone can see who won just by looking around the room.