Unless I am missing something one can't nest selects. Example:
select field1, ..., (select something from sometable where ...) as NestedField
FROM primarytable
It can be done through view or storedproc of course.
For typed lists you mean? That falls into the same category as expressions. We thought about it, wrote some test setups but it all turned out to be more work for the user than simply writing a couple of lines of code. I.o.w.: it would make you less productive.