I think unless iOS5 has something like SBSettings, bite SMS's quick reply, iFile and winterboard people will still jailbreak.
I love themes. I don't want my iphone UI to look like everyone elses. Whenever I've gotten a phone, the first thing I've done is theme is. Make it feel more like mine.
And I don't want to have to close whatever I'm doing, then go into messages just to reply to a text. quick reply is perfect.
And I truly hate being without SBSettings. Everything just seems to take longer without it. Turning on wifi, 3g, removing background apps. clearing safari etc.
I don't see myself every not jailbreaking unless apple integrate a huge amount of the available JB tweaks.
And TBH, Even of they do, there will be plenty of stuff we want to do but can't. I believe JB is here to stay.