X-23 has been given one more issue before being canceled. It will end with issue 21 in March, skipping February for the Venom Event. This news comes courtesy of commentor Arvelous finding it on Marjorie Liu's twitter feed.
You can find her responses both here and here. Where she says:
Not news anymore, but I can finally confirm, personally, that X-23 has been cancelled. It's bittersweet. I truly loved writing that book.
Oh, and it won't just be 20 issues, but instead *21* issues of X-23 (we're not shipping in February). @philnoto will be penciling both.
Again, from the bottom of my heart and those here from KP, we'd like to thank Marjorie Liu, Phil Noto, and Sana Takeda, for their time, dedication, and phenominal work. The care they put into the issues truly shows and the book will be greatly missed.
Come March, KP will be doing a follow up entry to commemorate this as well as what'll mark Marjorie Liu's second year as writing X-23, as the one shot released in March 2010 was her very first full issue of writing the character. The timing of this final issue brings us full circle in a fitting manner rather than just abruptly after January as it seemed.