I just spoke to motherof11 and you can release books with no E in the title or no E in the author name, so the rule is broader than when I ran the challenge. So a book with an E in the title and no E in the author name counts and vice versa. So more choice!
Much more, actually (and less of a challenge).
I just ran a counter on my own shelf and got that about 7.5% of all books on my shelf feature e-less titles but about 16.5% e-less authors. 1.5% belong to both categories. So with the new rules, the number of matching book triples.
This is a shelf with a majority of german books. Earlier evaluations showed that among german books the percentage of e-less titles is considerably lower than among english books, but I haven't got the numbers at hand. However, even among english books the number of matching books probably at least doubles with the new rules.