No active current plans for it with Invictus, but you’re not the first person I’ve seen interested in it so perhaps it’s something we can be open to (and something it’s I’d personally want to see).
It's another changing point in history (like Alexander's war with Persia) so I'm not surprised there are people interested in it. Early history of Christianity is very interesting to me and that's why I'd love to see it in the game, hopefully done with as great attention to historical details as the rest of the game and mod.
I'll expand on this a bit, we delayed the enddate to the 30th of December 1BC for no particular reason so you do get an extra 27years in the game.
Christianity is a contentious issue in history, so any extension further than 1BC of the enddate would most likely see only minimal Christian content.
Pushing the end date is quite easy, adding new content there is much more difficult, especially to those with little modding skills like me. Adding christianity would require adding a completely new religion to the game, proper "emerging" events and conditions and then some other things like decisions and events.
And "contentious"? It happened, we know more or less why and how it happened... It's just history.