While increasing lag would be bad, it's not the last thing the ICO community needs. The last thing it needs is to be divided further. These mods are great, but keeping everyone on the community running the same version is more important.
I don't think it would be a major impediment as long as people knew where to find the standard mod, which wouldn't be too hard to figure out. The big difference between a mod like this and Entrenchment is that you can download the mod for free. Thus, if someone wants to join a game they can't join they just simply get the mod. Also, you only need to get it once and people can easily turn the mod off if there aren't enough people around who want to play the mod.
What I might do is make a tinyURL link to it and try hosting some games with it, being able to easily type out the tinyURL link.
http://tinyurl.com/sinsplus
