Interfaith Gone Too Far?

This weekend I went to two different Eid potlucks. The first one was mainly geared towards dawah to the Christian invitees. I think dawah is great but filling up the whole night with it with no time for the muslims to converse with each other or the Christians seems counter-productive. On top of that I was shocked to hear the speakers' idea for interfaith activities. He suggested that muslims should do jumah prayer in the church and the Christians should come to the mosque and do their service there. Does anyone else have a problem with this? I couldn't believe what I was hearing. First of all as a former Christian, I just know that they are thinking that that would be an encroachment on their territory (this is going even beyond Little Mosque on the Prairie). As for Christians doing their service in the mosque, can you imagine shirk being preached in a mosque which is the only sin that Allah will never forgive? I think there is a point where you cross the line.  What say you?  The second potluck had absolutely no dawah as that mosque is very allergic to it and to prove it I got to sit all by myself at a table just for me and my kids. Ahh, the joys of being a convert.