I think the point of QUIC is 'if the implementation other using is problematic, I can use my own. And no random middlebox will prevent me from doing so' instead

I think the point of QUIC is 'if the implementation other using is problematic, I can use my own. And no random middlebox will prevent me from doing so' instead of `everyone must bring their own QUIC implementation.` There is a slight different here. It's the difference between 'the right to do' and 'the requirement to do'. While at same time. You must use 'system tcp implementation' and you are not allowed to use custom one. Because even system allow it (maybe require root permission or something), the middlebox won't.