The BOM is one of those things that seems like a neat idea at first, but has loads of problems. Like, if you concatenate files together, are you required to strip the BOMs first? If you have an embedded BOM in the middle of a file, does it mean anything? If it's reversed from what you had at the beginning of the file, should you change byte-ordering again?
And what about the unix hash-bang line... if you have a BOM in front of that, will it confuse things?
A lot of code would need to be re-written to deal with this simple little idea...