800 page upper limit

How strict is the 800 page upper limit for printed books? Is there a
way we can increase this limit (possibly for a higher price point)? I
don't want to say it's common, but I've already found one book that's
larger. Foundations of Education and Instructional Assessment, First
edition (there are three separate editions of it!!!) is a whopping 870
pages long, not including all the optional frontmatter that could have
been included. Obviously, for groups who have put so much effort into
their books, I would like to find a way for them to be able to buy and
enjoy them.

--Andrew Whitworth