Conflicting rules on differential pair length matching
Rule 2.1.8 says that 15 pairs per peripheral slot aren't length matched as they'll carry slow signals. However, in 2.1.9 a strict length matching is mentioned (of 5mm, or ~33ps). I suppose the latter can be either removed or relaxed (and 2.1.8 slightly modified in that case).
Also, it's not entirely clear to me if the length matching mentioned in 2.1.9 should apply within each differential pair or to the whole group of differential pairs that goes into each peripheral board, though that might be just me.