Adding scenes doesn't increase hourly capacity. They could run a flume out of the Norway building and connect it with all of Gran Fiesta Tour next door and then send the boats back to the Norway unload area, and it wouldn't increase the hourly capacity. It would just make the ride longer, and give you a view of the employee parking lot.
Hourly capacity is dictated by how many passengers are dispatched in a vehicle at what time interval. Example: 10 Passengers Dispatched Every 30 Seconds = 120 Riders Per Hour.
If Maelstrom dispatches a boat every 45 seconds, they get 80 boats into the ride per hour. If a Maelstrom boat seats 12 people the equation becomes: 80 x 12 = 960 Riders Per Hour
The on-ride YouTube videos available show that the boats are dispatched, and unloaded, roughly every 45 seconds. That gets you the "every seat filled" number of 960 riders per hour for Maelstrom. But since every seat isn't filled, some rows only have two people, and some boats take longer to load or unload, the real world numbers for Maelstrom were likely 850 to 900 riders per hour.
They could add an extra row to the boats, and that would get them up to a theoretical 1,200 per hour. (80 x 15 = 1,200) But probably closer to 1,100 per hour in the real world, with new boats with an extra row.
Otherwise, any additional capacity would require major changes to the ride system. And the track switch mid-ride that sends the boats backwards is the bottleneck there, as that operation requires 30+ seconds to perform. They'd need to engineer a faster track switch operation, or eliminate that and rework the flume to route around it and keep the boats pointed forward, to get any increase in capacity beyond 1,100 per hour.
But if Frozen Flume Ride is just a redressed version of Maelstrom using the same 12 passenger boats and same ride system, then 900 riders per hour is what you'll get. Nothing more.
As a point of reference, Pirates of the Caribbean at Disneyland has a theoretical hourly capacity of 3,400 riders per hour, but the real-world numbers are around 2,800 riders per hour because modern Americans can't fit four to a row anymore.
But 2,800 riders per hour is dramatically more than 900 riders per hour.
"Math is hard!" -Teen Talk Barbie, 1991