"Newton-successor" is definitely not the way Apple would or will describe it. The Newton was ahead of its time, great as a "proof of concept," but not a commercial success. That's not the way Apple wants to enter that territory again. Apple now knows how to "get it right," and I look forward to the release of their tablet whenever they decide it's ready.
Apple learned a lot with the Newton that much is for sure. And I completely agree that they would not want the new device, even if it looked, felt and smelled like a Newton to be called a Newton.
As someone who loves and still uses their Newtons (2000/2100), I long for the day for Apple to re-enter this market.
Unfortunately for Apple, the early Newtons 100 & 110 were rushed to the market and had many problems. The handwriting recognition was the worst. By the time they introduced the 2100 model, many improvements had been made and the handwriting recognition worked great. But by then it was too late, the market had spoken.
The Newton 2100s were built well. Mine are still working after 10 years. Some folks even use them for web page servers which is amazing.
IMHO, a PDA/Tablet requires a pen for input and needs a larger screen than the iPhone/Touch currently have. On a side note, the original Newton OS was very scalable, object oriented and future focused. There were plans for Newtons that ranged from around a 3x5 sticky to white board sized displays per the developer info that I had at the time. I really love the integration of the Newton OS. The iPhone/Touch are the closest that I've seen since, but alas they are not there yet.
The Newton 2100's screen was a wonderful size. Dreaming here. But a Newton 2100 with color screen and about a quarter to half inch thick would have been nice. Of course it would have built in WiFi and BT.
Hopefully, Apple will one day re-enter this market.