I do see the benefits of a wireshark plugin. However, I decided against it because of the user interface constraints. With the current x11vis GUI, I am free to develop in any direction that I see fit. I especially thought of displaying the different x11 clients next to each other horizontally (useful on big monitors only), for example :).
I am also not sure if wireshark allows packages to be modified afterwards. x11vis kind of jumps back to modify packages as soon as it gets new information.