How much dating experience did you and your wife have prior to getting together and marrying ?
Pushing for a change in your relationship for some guy staying in your house after 5 days seems so impulsive and perhaps dangerous and very short sighted.
I think she really really need to understand that going down this road is a 2 way road. Traffic will run both ways. I always love the concessions people will make to get what they want but never really think it through fully ....until its too late.
But if you want an open relationship ....you got to start somewhere.