If I remember right, the news was first that Chris Claremont wrote a treatment and then Josh Zetumer wrote the screenplay. I remember a couple sources saying that it was a good script and they started auditioning Rebecca Ferguson, Abby Lee, and Lea Seydoux for Belladonna and articles reported that it was a highly contested role. Lea Seydoux landed the role and I believe after this is when the rumor of Channing Tatum leaving the project came out. And even though it was reported that that rumor was totally false a few days later after he officially signed on, from that point on all the negativity and delays followed including Rupert Wyatt dropping out months later.
So I wonder if the script being reported on was this first script they seemed to be going with for a bit. Seems likely.