Yes, the control panel is replaceable, so is the complete software.
But...I don't see any need to create alternative software for the Chumby, yet. It has been done with other devices that can run Linux, and I think it will be done in the future again. The driving reasons behind doing so have always been (a) to see that it can be done and/or (b) to open the device to do things the hardware manufacturer did not allow it to do.
With the CHumby, (a) has been done. And for (b), at the moment chumby industries is responsive and willing to include new features.
Also, with the other devices we have seen that it takes an incredible amount of man hours to do so. Some of these "hacks" have been around for many years---and are still not stable, nice looking or feature-complete.
So for now, let's try to convince chumby industries to make the Chumby better.
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BTW: I'd like to point out, that most of my suggestions can be implemented by GUI changes. Only the "station presets" require changes to the structure. And even there much of the existing code from the alarms can be re-used.
C1 user in Germany