I guess in the end the question is - would it really be smart for S-E to look at this example and want to do it too?
The best thing I'd take away from this, in terms of Square-Enix's thinking, is exactly the numbers you mentioned in there.
DS version = Decent numbers? (Not what Level 5 had hoped for, but not a bad showing for a new IP)
PS3 version = Western success? (Haven't seen anything showing otherwise really).
Although I realise there are issues with what L5 were expecting for NiNoKuni, DQIX showed that a handheld mainline Dragon Quest can certainly be well received (and sell well) in Japan.
And then a PS4 version, you'd hope, would be able to replicate at least a similar success (if not better) in the west, while gaining some sales in Japan.
Besides, some of the issues with NNK seem to be based in other stuff (delays in development of PS3 version; magic book-based DS version etc.) which wouldn't necessarily plague DQXI.
But regardless - the only reason I'm bringing is up is because of what we're hearing about the game. Everything that gets mentioned about DQXI seems to be suggesting that they
want to make a home console version. But I don't see any conceivable way they can to keep the IP in line with what it has historically sold.
So this would be a method for them to achieve that
and release the game on the console which has pretty much been the home of Dragon Quest for the last 3 years.