GHC already does a lot of loop fusion and optimizing away of linked lists (which is good given the unfortunate overdue of cons-lists over nicer things among Haskell users) which can be extended to work with user code using rewrite rules. Libraries like text, bytestring, and vector do exactly the elision of intermediate structures that you talk about, allowing you to convert from a vector to a list, apply some function that annoyingly only works with lists, and convert back into a vector, and have that compile into a single tight for-loop in many cases.

I wonder what the upcoming linear types work will do.