While I struggle to commit to 'never' as that's a very long time I agree in principle.
The big barrier is the nature of the console business with exclusives.
Halo has a huge fanbase and that is locked into the 360. To achieve sales similar to Halo Sony has to release an FPS so good that it can achieve one of the following:
a) convince a large percentage of 360 owners they must have a PS3 too just to play this one amazing FPS - that's a pretty tall order.
b) release an FPS that appeals somehow to people who want to play FPS titles on a console and don't have 360 / Halo - again, if you think about it that's a pretty tall order.
c) a bit of both - maybe slightly more chance with this, but still tough. You need an FPS that's different enough to interest a huge number of people who don't like Halo or have 360 and manages to pull in some 360 owners are well
In terms of a GT killer I think this would be tough for MS but not quite as hard. I'm going out on a limb here, but I think that while a lot of Halo / 360 fans would simply reject (being the hot headed folks they are) the idea of embracing a PS3 FPS to the same level - driving fans are not so 'die hard' and it is probably easier to lure driving fans to 360 than FPS fans to PS3.
But yeah, the basic principle is sound - matching an exclusive killer app is really, really tough as the competition in a sense already has a big chunk of the potential player base sewn up in their favor.
As others have noted, however, beating Halo sales for multi-platform titles is more than possible.
