I, for one, like the idea of an ARM processor on a board in the same form factor as the Arduino.
I would have designed such a board a bit differently though, and am thinking I have a good idea now. I would have put another row of headers on the outside of the Arduino headers that would allow for extended shields that could use more of the ARM processors I/O resources. Standard Arduino shields could still be used, as well as extended shields that would also plug into the extra headers.
I run out of I/O real fast for the stuff I want to do (robotics mainly, but other projects also). I also would enjoy something that can at least do fast task switching, if not true multitasking and scheduling. I have a couple of ARM7 boards that use the NXP LPC2148, which I like.
There has already been somewhat of an effort to port the Arduino environment to ARM9, and some work has been done to make it all work for libraries too. No, it's not my effort, but I know the people who have worked on it, and the effort is currently on hold. I don't know if the IDE has been addressed or not though.
I'm involved with a project to create a new IDE for the Arduino that will be extendable, and written in Python instead of JAVA. I don't care for the way things happen in the current IDE, such as not properly preserving tabs and not allowing the length of tab stops to be changed to suit an individual style or need. I also don't like breaking standard language features (such as casting) just to make it so a lot of people don't have to learn at least some of the language's features.
This is just me though, and I am not new to programming. That's why I dislike seeing efforts to do what I consider watering down language language features.
There has to be a medium where new folks can get online with Arduino easily, yet those of us who are not new to software development won't be insulted. New folks should be able to come up to speed fairly easily and learn more if they want to. Maybe the current Arduino market and community are being underestimated in what they are able to do and/or want to do.
I'm just getting into creating libraries for the Arduino, and am having some problems I'm not at all sure are within my code. I just don't have the confidence in the Arduino development environment I believe should be there.
If the current environment had a plugin type of architecture, it should be a lot easier to define new boards, including such things as setting the toolchain, debugger, and other processor specific items.
Apologies for the long post. These are things I have been doing a lot of thought on.