According to Kaphotics on Twitter, in DPPt, there is a 98% chance your PokeRadar chain will continue when catching a Pokemon 4 grass tiles away, but in BDSP, there is a 93% chance in the same situation.
Doing the math, (0.93^40, 0.98^40,) you have a 5.49% chance of getting to a chain of 40 in BDSP, while you have a staggering 44.57% chance of getting to a chain of 40 in DPPt.
Keeping in mind the other changes to the PokeRadar, (universal 4 patches and that subsequent Pokemon in a chain will always be the same species,) does this mean you are better off shiny hunting in Diamond, Pearl, and Platinum?