Monkey World already have 2 breeding groups and 2 growing males and so would have to build separate accommodation for Kevin.
That is correct. So I can understand them asking for funds to build an enclosure especially as Berlin must be a wealthy Zoo- though splitting the cost might seem fairer overall. It would seem an obvious place for him to go as they could provide him with a partner for breeding etc and though they would have to explain his condition to the visitors that's fair enough being as they are a 'rescue' organisation.
I imagine no other Zoo will take Kevin as an exhibit, so Berlin might just end up euthanasing him eventually if they can't rehome him as he is clearly just a nuisance animal to them.