The more time I spend thinking about this... the less I actually like it. Splitting the series into two formats is such a gamble. And the downside massively outweighs the upside.
The Dark Tower has a built in audience, to be sure, but what about new fans? Are people going to commit to this idea? It'll be like watching every other season of LOST in a movie theatre. It'll be difficult to keep this from being too confusing. The series is hard enough already.