I must admit the word "fun" is not what comes to mind. It makes it seem too easy.
Yes, it would be potentially fulfilling and achieve a level of closeness we all are striving for in my "V" but it comes with challenges. Challenges I am not prepared for yet and may never be. There are much more experienced fully polyamorous Vs from which to draw on. My situation is a little different due to the mono/poly nature of my relationship. That in itself poses a whole body of challenges possibly above the norm.
"Fun" sounds like a juvenile approach to a very serious step in any relationship.