It seems like the official name of the expanded Mandai precinct will be "Mandai Wildlife Reserve". I understand that the existing River Safari will also be renamed. The changes should happen before the end of the year.
To add on, River Safari will be renamed River Wonders and all the parks will get new logos with a consistent design aesthetic and font - though i'm not sure if the new Bird Paradise (this is apparently the new bird park's official name) logo will be used for Jurong or if it will stick to its existing logo till the end.