hmmmm.... maybe the N53 engine will make it into the MY08 E60, which is the refresh year for that car.
A 528i with the N53 engine and DI would be a great base engine upgrade over the existing 525i, and would get it to near current N52 530i performance levels. Then a 535i could fit nicely in the pricing lineup between the 528 and the 550. Right now there's only about a $3000 difference between the 525 and 530, but a much larger gap between the 530 and 550. So maybe a 528/535/550 lineup makes sense afterall.
If they do that, and the 528 is the N53/DI, I'd probably go for one of those as opposed to a 535. I think the non-DI 528 would be a tad soft for me, and then I'd probably get the 535.