Honestly, I'm not convinced $ENV{HOME} should be used on any platform, other than maybe for test purposes. That said, the method of finding specific directory types on Darwin is awfully convoluted - I'm wondering what changing $ENV{HOME} would do when you're looking for a specific type of directory using Mac::Files::FindFolder...
Assuming that you apply the same tests with and without $ENV{HOME} set - including nonsensical values, and that said tests are submitted with your patch, I don't see why Adam would say no. Mind you, I've got a larger patch sitting in his queue at the moment from the beginning of November that hasn't made it in, so I'm not sure what RL is doing to him at the moment.