Kind of like “what would you do for the excel abuse case in an environment not tied down by decades of legacy compat?"
That was my first impression (seeing this for the first time today). In an "all built on top of js" world you might just make a snapshot of the entire stack (except for the "browser substitute") part of the document. Make "open new document" essentially the equivalent of github fork from an ever evolving "the empty document" template. You might see quite an impressive reward from moving fast and breaking things instead of sticking to the paradigm of eternal 20th century compatibility.
That was my first impression (seeing this for the first time today). In an "all built on top of js" world you might just make a snapshot of the entire stack (except for the "browser substitute") part of the document. Make "open new document" essentially the equivalent of github fork from an ever evolving "the empty document" template. You might see quite an impressive reward from moving fast and breaking things instead of sticking to the paradigm of eternal 20th century compatibility.