I think they'll have no choice but to respond with something like it at a comparable price.
BIS is enough for me except for one thing: remote wiping. I'm self employed and don't need my work computers to be wirelessly updated with contact and schedule changes. But remote wipe, which Apple's upcoming MobileMe software supports, would would really be nice to have.
Yes I know there are 3rd party BES providers I can use but the cheapest I've found (that I trust) is $20 a month, plus I'd have to upgrade my Verizon plan at $10-14 a month to use it. Way too much but I understand why:
I talked to my web hosting provider, where all of my business email goes through. They've been struggling to find a way to make it happen but RIM makes it impossible since they use Apache (that's a good thing). They tell me they'd have literally rebuild their entire email infrastructure around MS Exchange and raise their rates because it's a nightmare to setup and support.
But I don't need CIA-grade security. RIM could implement this through BIS if they wanted to but it wouldn't be as secure as BES. Which is fine; they could do both: continue to offer BES for those who need it, and enable BIS to do what MobileMe does.
And like I said, they probably will.