Having just moved one large carnivore off the mappins I really doubt they'll plan to install another, as we keep going back to the fact that there is virtually no opportunity to create decent indoor space on the terraces themselves, plus the height of the barriers required might even interfere with the listed status, especially given that the one of the major current drawbacks at ZSL are the singular outdoor enclosures for their two big cat species. I can't imagine the mappins separated into high-fenced paddocks somehow.
The lion terraces are such a bad use of space that it would be entirely possible to create larger compounds for both species. From a welfare perspective, it would be better though if, as people suggest, the vast area along the North bank were utilised for one cat species, where the crane paddocks used to be. Or they should just make three island pond the second tiger paddock, I don't think they're likely to breed from either flamingoes or pelicans in that enclosure....
The idea that you can ask visitors and supporters, who already pay £15 when entering the zoo (with an optional £1.50 added on for 'tiger conservation') to help pay for ZSL to whip up a fanciful trail through the Indonesian rainforest, is totally ridiculous. It doesn't cost 5 million to house tigers in decent enclosures elsewhere in captivity, so why should it do so at a collection which makes such a big deal out of the in situ work it does yet has long-owed it's two non-breeding, slightly disturbed Sumatran tigers just a decent outdoor enclosure with some height, privacy, separation and space, not some disneyfied 'experience' with lots of glass and contemporary design....paid for by public appeals and taking longer due to the costs involved.
At least the females are being swapped back, I never thought I'd think it was a good idea to send anything to Dudley, but in this case it is the best thing they can do for now.