My thought (mostly guesses, rather than backed by data)
I'm finding it difficult to judge what the EB3-ROW demand actually is (and might be in the future).
I'm undecided as to whether EB3-ROW will become Current in FY2015. The number of existing cases falling through to FY2015, plus cases with a PD from October 2012 onwards might just prevent EB3-ROW becoming Current in FY2015. That said, because of processing times (both PERM and I-140/I-485), the date can be ahead of actual numbers, so it could happen. I think it will be close either way. On balance, I think there is a possibility towards the end of FY2015.
When the EB3-ROW dates move beyond 01OCT12 will depend on how many cases fall through to FY2015 and how many visas CO believes he has available for EB3-ROW in Q1 FY2015.
As EB3-I receives Fall Across, then the COD will start to move ahead faster, but there will still be a considerable underlying gap in PD between EB2-I and EB3-I for several years. It may reduce porting over time, but not eliminate it IMO. It will take at least a year for the numbers to slow, because the process has already started for the next batch and very few would become current under EB3-I even if the dates moved forward. The EB-C situation was different, since the EB3 COD was actually ahead of the EB2 COD and reverse porting has occurred.
I guess your point is that that more applications will be received in EB3-ROW as dates move forward rapidly, reducing EB2-ROW approvals and providing more Fall Across within EB2 to EB2-I.
That is an important consideration, both for Fall Across to EB3-I and for EB2-I. An increase will eventually reduce the Fall Across available to EB3-I. At the same time, it also reduces the chances of the Armageddon scenario because EB2-I would receive more Fall Across within EB2.