From the sounds of it, the Jumeirah property would have to be on the Thonburi side, as I don't think there's a large enough lot on the Bangkok side to hold a resort such as that described. Possible, though, especially if not in the densely packed stretch from ROS to Saphan Taksin.
The last time I was in Bangkok, it looked like the Pepsi bottling/distributing facility on the Thonburi side, next to The River condo block, was shutting down. Is there any word that the Pepsi facility is slated for redevelopment into a hotel or resort or residential property?
Any one of these could be the long-awaited, much-wanted, rampantly rumored aman Bangkok.