Based on the changes in PM-1309 (change WT data format to track history), it's possible for a Btree leaf page to appear empty. For example, after a MongoDB downgrade or close/re-open, where every element on a page has a set stop-timestamp or stop-txnID, the page will be read but will subsequently appear empty.

I don't know if that is guaranteed to work in the existing Btree implementation and it needs consideration.