I have 3000 books loaded into Calibre of which 900 are on my Kindle still to be read. Once I have read a book, I remove it from the Kindle. I still have over 1500 books that are not on the Kindle.
In other words, if I never acquire another book, it will take me just short of forever to get thru my TBR list. This is the grand scheme of things is not a bad thing in my mind.