Well, the Casson does have two substantial hospital dens built for elephants and rhinos. So the indoor dens
could be adapted for night accommodation. I think this was being talked about on a back of an envelope basis about 12-15 years ago, maybe not very seriously.
The real problem would surely be the exterior, built for resolutely terrestrial large mammals and now presumably with some planning restrictions attached. How that could be turned into something stimulating enough and secure enough for orangs I don't know.
On a more personal note: at no stage have I
EVER said that I want London to go back to how it was thirty years ago. Personally I feel that the elephants should have gone in the mid 1970s, that the Sobells should never have had more than two species of Great Ape after Guy's demise in 1978, and that the Lion Terraces would have worked better if built to house only three species of big cat, rather than the original five.
It is not being "
negative" to criticise and suggest that the present policies of management
may not be the best way forward. Anyone who's looked at my posts will see that they're overloaded with suggestions for exhibit ideas at Regent's Park, and for that matter Whipsnade; planning within ZSL is surely best accomplished on the basis of "one collection, two sites". This may be the hallmark of an overactive mind

, but I don't see that it's that of a negative one.
I am reminded, in conclusion, of scene in "A Man For All Seasons". Sir Thomas More has been summoned to Hampton Court, where Cardinal Wolsey wishes to win him over to support his policy of securing Henry VIII a divorce.
Wolsey, as an introduction, says to More: "You opposed me today in Council today, Thomas. You were the only one. Why ?"
More's response is quite simple. "I thought Your Grace was wrong".