[hardwaregeek]

This is true, but a lot of users will clamor for a 30% solution as well. A user may be writing a back end in your language and ask for first class SQL. After all, they write a lot of SQL and being able to have typechecked, safe SQL statements sounds great, right? Except, not everybody writes SQL. Indeed, SQL may be dead in 10 years (I'm not making this claim, but it is a possibility) and replaced by a different language.

A good language designer will see that users want a general way to query over data, and create something like LINQ.

Of course, you're right that language designers shouldn't go for a 100% solution. Monads are kind of the classic 100% solution. You can do anything with monads, but that means you can do anything with monads.