A native 'decimal' type for Java replacing the BigDecimal class would be nice. But Java thread-safe collections are nice.
Perhaps the question is not so much what Java 7 needs to persuade developers to use it, but more a case of what makes developers want to move from Enterprise/server-side java language to a different C# desktop Windows-only oriented world?
For most developers, the language isn't difficult to pick up be it Java or C#. I develop in Java, but Linq didn't take long to understand and use.
I think the choice of Java or C# depends on what motivates you personally -perhaps money? in which case either language will do whether they have certain features or not.
Ste