I'm not sure what the numbers are, but after the initial rush of sales, I'd bet the 9R and Boost end up at no more than a third of Poo's sales. Just in terms of offering something to everybody, I'd like to see them do what Polaris is doing. The 850 has been a pretty good motor (I'd still prefer a little more bulletproof, but it's way better than the Dragon/CFI 800s), and it's great they're offering the 9R for those who want it. It's hard to tell if Cat can justify more than two motors though, and it seems to me that 900cc is at the point of diminishing returns: you do get more power, but you're trading off a significant amount of engine life. Where you're at on that trade-off depends on your budget and priorities; for me, even 50% longer engine life is worth more than another 5-10 HP. And that's based on the weight of something like my Pro. If Cat can really undercut Polaris on weight, an 850 would feel the same or better than the 9R.
I do see a strong possibility in what
@summ8rmk suggested: maybe if they made a 900-ish motor, but not significantly oversquare, more like the Doo 850. Imposing a strict RPM limit (say, 8000) could allow for a bigger motor and bragging rights with it, but similar life to either 850. That would probably leave them down five or so horsepower to the 9R, but give it similar, possibly better, mid-range and responsiveness. It's hard to predict because the rush of big motors fifteen years ago didn't produce anything you'd want, but maybe the technology just wasn't there yet.