Problems occur if two extensions conflict -- i.e.: if the tests for two different extensions both return true on an input. However, this can easily be modified to create some sort of alert if that's the case.
Problems can also occur if one person's code only works with a certain extension not in place. A solution would probably involve some sort of scoping mechanism like
Having the tests for two extensions return true for an input can be useful, for example if you have a specific case and a general case. By loading the specific extension after the general extension, the specific one will override the general one.
