I just don't see it as something Kate would do either - I see her as the 'insanely jealous' type and don't think she would actually be able to let Jon do that - she would have to control who he would see!
I think she wouldn't do it - not even for the show, she's the type who would kick him out and then go for the 'Kate as single mom with 8' brand!
If Jodi and Kevin don't think this is going to blow up in their faces big time they are either very naive or very dumb. As said been said numerous times (usually about Kate), if you put yourself out there - you open yourself up to major criticism.
The media will start sniffing around them and I'm just waiting for the 'scandal' about them to erupt. If there is anything even remotely iffy about them, the media will find it. And I will have absolutely NO sympathy for them.