I can't imagine a way that #1, #2 or #4 would be able to "break the web". Worse case scenario is they add a tiny amount of overhead. #3 might cause a tiny minor

I can't imagine a way that #1, #2 or #4 would be able to "break the web". Worse case scenario is they add a tiny amount of overhead. #3 might cause a tiny minority of websites to stop working, but they'd get fixed quickly if #3 was implemented.