The fact that NO ONE in the past 14 years has followed up on Christian means that no other writer has been interested enough to do so, to devote even a little part of their story to a follow up. If Sina Grace didn't do it, then who would? Because Emma was a major player on the X-men for years and no one ever bothered, not Whedon, not Fraction, not Gillen, not Bendis, not Lemire, not Bunn.
Plus I think there's something to be said about a one and done story. People have been complaining about how decompressed comic book storytelling has become for years now, story arcs that are written for the trade and stretched to 6 issues just to make last longer when the story could easily be told in a single issue.
We finally get some compressed storytelling and now they should have taken more time with it?
Another writer can take more time later to flesh it out