With Wizarding Worlds slated to open in Japan in 2014 and Hollywood in 2016, Singapore will be the only park left out. Nonetheless, I am convinced that plans are already on the way to add the Wizarding World in the future (perhaps long term) as it can really spike up the park's below-expectation attendance.
I think given the available land, there are 2 possible options for USS to add Harry Potter. Please first take note that I am not affiliated with RWS or USS.
OPTION 1: Behind New York (Diagon Alley)
There is actually an unused piece of land in between Transformers The Ride and Sesame Street in USS. While not the largest plot, I think it is large enough to fit more than 1 single ride, so a scaled down version of Diagon Alley will fit well there. Potential opening: 2016
This set of doors looks almost like a prepared entrance to a future attraction
Site of available land at New York
Schematic of a possible USS Diagon Alley
Advantages
+Do not need to eliminate any existing attractions
+Much lower cost due to the small area and fewer features, estimate SGD60 million
+It is too wasteful to commit such a large area to a single ride (vs a themed land)
+Escape from Gringotts is a less common ride (only 1 vs 3 for Forbidden Journey)
+Escape from Gringotts is a less common ride (only 1 vs 3 for Forbidden Journey)
Disadvantages
-Not much variety, only 1 ride and a couple of shops
-Transition into the themed land will be far too sudden as it is directly tied to New York
-Escape from Gringotts is almost a too similar ride system to Revenge of the Mummy
OPTION 2: Get rid of Madagascar
Madagascar themed area is a big waste of space to me. The main attraction, A Crate Adventure is not very popular (there are many empty boats) and the park puts only 2 rides in such a large area. A Harry Potter world here will most likely be themed to Hogsmeade and will include a family ride (Forbidden Journey), 2 thrill rides (B&M flier and drop tower) and a kids section (Softball play area). This makes the Singapore version of Harry Potter the most family friendly and diverse targeting version. Potential opening: 2018
Map of the current Madagascar
Schematic diagram of Hogsmeade at USS
Advantages
+It will be the best version of the Wizarding World of Harry Potter with the broadest target audience
+Addition of Owl's Flight means it is alright for Battlestar Galactica to go and make way for a more reliable ride
+Much more immersive experience with genuine Hogsmeade Main Street and a forested area leading to Hogwarts and the thrill rides
+USS does not currently have a drop tower, robotic arm ride nor children play area
+For coaster fans, it will have South East Asia's first B&M Roller Coaster
Disadvantages
-Bad news to all Madagascar fans - it has to go
-May take longer before completion due to the need to demolish then build
-Definitely very, very expensive. We are talking about a SGD200 million range at least
I know that most people would rather see Harry Potter come to USS, so please share this link with all your friends so people will know. If enough people are aware and have a desire for The Wizarding World, RWS may just well decide to bring it here. To be honest, I really, really prefer option 2. Please reply and tell me which option you prefer.