The odd shape of the park is due to the fact that it is cannibalizing on Singapore Zoo land (top half) and Night Safari land (bottom half). This is the largest and clearest image I could find online.
Image courtesy of Icon International Communications.
I think the tigers were going to be Malayan rather than Sumatran. The one thing I can't recall is what other species were going to be down there, not many I think?
The major exhibits all materialized, but many of the smaller aquarium and terrarium displays were shelved or scaled down. And there was the Murray River zone which was never fully fleshed out and is being replaced by the new mangrove/coastal display.
The area below the rapids ride was supposed to be part of a "Temasek River" zone. Temasek was the pre-14th century name for Singapore, and that zone was to have displayed species that are or were native to Singapore. Listed species were Malayan Tiger, Mousedeer, Prevost's Squirrel and Reticulated Python.
I understand that a third boat ride attraction is part of the next phase of development, but i'm not sure if it will be a rapids ride. The area on the map where the rapids ride was to be located is currently unused land.
Haven't heard of any plans to revive the Temasek River idea. The area on the map where the tiger enclosure and trail were to be located is now the Asian elephant paddock seen from the River Safari Cruise. The paddock is supposed to be an interim exhibit, and the area will be used for park expansion when needed.