I think if Apple does a tablet, it'll be a big iPod Touch not a small Mac. The market place just hasn't embraced tablet PC's. The manufacturers keep trying over and over and it just doesn't catch on.
I think your hypothesis is flawed. Tablets haven't taken off at this time, therefore it will probably not happen. Not saying that it won't, as science is never exact.
Roadmap ? Apple wouldn't know a roadmap if it slapped them upside the head. Info flows more freely out of North Korea than it does from Cupertino about upcoming computers. It really is annoying trying to purchase computers from Apple wearing a blindfold. Screw all these silly special events. Just issue a press release, build the d^^^^ computers, and ship them as soon as everybody else ships theirs. Enough with all the cute games already. Geez, grow up Steve, will ya.