In effect, that is what I did when I purchased a 2020 with the ISB. However, the difference between the flat torque curve on the ISV with 600 ft-lbs max and the 700 ft-lb peaked curve of the ISB is not as much of an improvement as most would expect from a 65hp increase.
The culprit is quite likely a combination of the torque limiting software in place to protect the Allison 2500 and the gear ratio fitment.
So, if you do seriously consider a swap, budget for the 360HP ISB with the Allison 3000 and any upgrade in differential gearing necessary to handle the increase in torque needed to deliver performance to expectation.
Alternatively, look at replacing the 6 speed Allison with the ten speed Allison to better utilize available torque. That package may well be available down the road and would make an excellent upgrade.
Alternatively and recommended ..... enjoy your coach. Dampen your expectations. Accept the capability, adjust to that reality, and travel with a smile.
Travel Safe and with a Smile! Pat