I don't debate AT ALL there must be *something* within a long term R that keeps things interesting. But (IMO of course) what Future's W wants is the option to "chase" other men if she feels like it AND have Future as her husband. IMO that cannot really continue in a marriage if that is the road they get on yet Mrs. Future seems to suggest/hope (if I am understanding all of this correctly) that it might work for them.
To me a "regular R" or "regular marriage" does not involve ANY third parties! The "dance" should be between two people (husband and wife, boyfriend and girlfriend or whatever the case may be) but not a husband/wife and somebody else when things get boring. Unless I am totally misunderstanding all of this it seems Mrs. Futre is wanting a very "modern" framework to the marriage.