[O]ne should still expect a high degree of cooperation in the just-elected legislature. Despite historic hostilities between the PRI and PAN, neither party ran campaigns that were so insular that they would breed increased polarization or enhanced divergence in their political agendas.
I'm not sure what exactly is meant by "insular", but the conventional wisdom (backed up Beltrones' comments since the election) is that the PRI will be less likely to cooperate precisely because of the PAN's electoral head butts, at least in the short term. And it remains to be seen exactly how much overlap there is in the PAN's and PRI's priorities, but so far, specifically with regard to tax reform, the two parties are at odds. We'll see how long it lasts, but I don't think that what we've seen since the election leads to the conclusion that the parties are ready to roll up their sleeves and work together.