Yes, i think that all new OSPF links should be Dual Polarity, and it’s certainly what I would do personally, but there’s a caveat. Shouldn’t some of the old “outcast” equipment go back into the network for those who cant afford to buy kit. If that is the case then how can you stop the beneficiaries of this equipment from using it on backbone links.
Based on the above, I think it goes back to our favourite discussion OSPF Costing Models as this is a technical way to cater for slow/single polarity links.