#9051 is one example of a current issue due to SegWit features apparently starting too early. Until SegWit is voted in (at 95% of the mining vote), I would expect that there should not be any rejecting of non-SegWit nodes, such as preferential peering or rejection of standard blocks - both of which seem to have already started happening with recent releases of Bitcoin Core.
What does the function IsWitnessEnabled() mean, for example? I would have thought this means that the 95% mining vote has been reached, but according to recent news articles this hasn't happened yet, so why is this function returning true?