This was being discussed in the possible Fallout 4 DLCs thread:
But The Abbey of the Road looks to be the most likely feature for a coming DLC. Its basically the only place in-lore that we know is close to the Commonwealth. Marcella says its just west of it.
Alternatively, we may just see missionaries or individuals associated with the Abbey in a DLC. Not unlike Honest Hearts and Joshua Graham/Daniel. That would be interesting as well.
While there is nothing preventing someone making something like this via mods, we are not allowed to discuss any real life religion here on the forum.