I think they generally have a rail that sits close to the wall and the seat folds up to also be close to the wall. So, I would not expect much reduction in width or inconvenience to others.
I think this is the sort of thing that could be approved subject to a condition that ‘the unit owner at any time of lot X is responsible for all costs involved in its installation, repair, maintenance and decommissioning when no longer required’. That wording means that if the present owner dies or sells the unit, the responsibility remains with whoever buys or inherits the unit.