Tread wear is usually not the reason for RV tire replacement. RV tires should be replaced at 6-7 years of age, and at that age the average RV tire is only half worn out. You can reduce the ozone damage (sun rot) on your tires by covering your tires when parked and by using tires that are compounded with ozone reistant sidewalls.
As for as the issues with changing from 275/70R22.5 to 275/80R22.5 tires, there is a size difference in that the 275/80 tires are about 2.2 inches larger in diameter. You will have to be certain that you have the clerance for the 1 inch plus radius increase throughout your full turning radius and suspension travel.
The different size tires will not have the same load rating. Since load capacity is critical on some coaches, you should weigh your coach and be certain that the tires will not be overloaded.
Gerald