Try to get an accessible cabin, but if you end up having to park it in the hallway don't feel guilty about others having to walk by it- housekeeping carts (bigger than ECVs) are constantly parked in the hallways, too, & that's never done anyone any harm.
Please don't take this advice. We sailed with my parents who have mobility issues and we had travel wheelchairs for them (we had done this several times so we know to pack patience). Going down the hallways any time during the day was difficult. One sailing, neighbors made this aggravating. Whenever they were in their room, they would park their ECV right outside their door. Early in the cruise, they saw us maneuvering the wheelchairs and just watched as we struggled because the woman using the ECV had no idea how to operate it to get out of our way. We tried to be patient. But by day 2 we spoke to our stateroom host about it being parked outside the room and he told us that they had been notified that they couldn't keep it there but did anyway. More than once we had to have my parents get out of the wheelchairs to walk the last part to their room and climb around it. Fortunately they were able to walk the 20-30 feet, but that caused us on a number of occasions to be blocking the hallway for several minutes, keeping other families from getting to their destination. (The other families were more than patient with us but we were trying to be courteous to others and it was frustrating that this one family felt their convenience was more important than the rest of us.)
My advice to you if you decide to take an ECV is to try to use elevators either before or after peak times. If going to dinner, head there a little early so the crowd for the elevator is not as large as it will be just beforehand. After the show, don't use the elevators closest to the theater or wait 10-15 minutes and they will clear out dramatically. And pack your patience. While most people will assist you, there will be a number of people who won't see that you are waiting and will jump on an elevator before you can even get there.