Disney already adjusts the number of buses on certain routes based on need. Not necessarily succesfully, mind you
The Artics actually handle pretty well - they can make it around Boston, which can't be easier than WDW
I would expect them to be on limited, busy routes - notably POP and the combined All-Stars routes, and probably AoA.
The main problem is the length, which is about 50% longer. At the typical stacked stalls at the parks and some resorts, this would overlap the stall behind it by enough of a margin to prevent the bus behind from being able to pull out. They would have to restrict them to certain stalls (like the last one) where possible, or rework some stalls.
Another possible change that might need to be made might be for the wheelchair access. All WDW buses have the loading at the rear door, but Nova's default config on the artics is at the front.
I also believe the model being tested is the LFS Artic, the LFX is for BRT applications, typically on restricted right-of-way applications.