After some test, still not very sure for this. TextNut is slightly with others, when user select a document, it immediately move focus to editor area, so user can continue to writing without clicking the editor again. TextNut remembers last editing position so user easily found where is last editing.
Although it is easy to add keyboard deletion on document, at above case, user needs to click the document cell again, so editor transfer the focus to document list cell, then CMD-Del can be functional on document rather than text.
For most other software, it won't focus to editor after click - so user can delete the document by keyboard immediately.
For a tradeoff solution, I can add CMD-del to delete document - however, user must ensure their focus is in document list rather on editor. Let's see if it goes well..