If you mean having the ability to use a pre rendered island based on some simple options that you choose, like size, mountains, tree volume, I think no.
It has been stated that for JWE2 we are moving off the islands to the mainland. I do think Isla Nublar and Sorna will be included, needed for Chaos Theory, which should make them avaible in sandbox.
The pre rendered with options maps are soooo obsolete given what can be accomplished with the terrain tools in JWE1. I expect more creativity with enhanced terrain tools in JWE2.
Don't forget that maps are going to be bigger, I fear not for just creativities sake, but as a necessity due the Territory requirements of the dinos, but depending upon the terrain tools and your imagination, sandbox mode will be the mode everyone will spend the most time in, eventually.