One of the common battles which we continue to fight as an accident of history is that of line endings. Even though we can take measures such as autocrlf policies and .gitattributes to try and eradicate the pain, it's a nuisance which keeps biting.
A feature which I think would help a lot, is the ability to see line endings in the GitHub UI. The default can stay as is (no line endings shown), but it would be great to have a toggle which allows me to switch on visible line endings in my view. This would be great in all file views, not only the standard view but also in the diff view when looking at commits, pull requests, etc.
As for a graphical representation, I think something like what TortoiseMerge does would be nice, i.e. a straight downward arrow for LF and a right angled arrow for CRLF. E.g. http://adamralph.com/img/eol.png
Whatever representation is chosen it just needs to be clearly distinguishable and obvious which is which.
Regards Adam