(taken from a post I made earlier on the Palm Entrepreneurs' Forum mailing list)
Q: Is PalmSource abandoning the PACE-like approach for OS6? Is it true that today's prc binaries will not run on an OS6 device? A"simple recompile" (as if that were possible) is going to be required to create an OS6 binary?
A: Current applications that work well on OS 5 should continue to work well on Palm OS Cobalt. If you don't need to use the new features of OS 6, I'd recommend staying with OS 5 development to maximize the market for your programs. PACE Native Objects will continue to work "if and only if" you're calling the OS through the 68K callback pointer, not making native calls. The main trouble areas will be relying on notifications to hook into the OS, patching traps (an OS 5 trouble spot as well), and the need to handle frmUpdateEvent in more situations.
Most of OS 6's new features are only available through the new API set, called "Protein". This is an ARM-native application model that allows multithreading, has no issues with segment size or global variables, and provides access to the new OS functionality. PalmSource has produced their own tools for targeting Protein, and they are included in the Palm OS Developer Suite.
Many applications can be rebuilt fairly easily. It's not a 'recompile', but more like a compile, fix errors, and recompile process. For example, APIs that used to take a card number like DmFindDatabase now omit that parameter. The OS 3.5 SDK names for types like UInt32 have been replaced by the ISO C standard names from <stdint.h> like uint32_t. A lot of developers got their applications running as native applications in an evening at the labs at PalmSource 2004.