You don't need an SDK to make programs for most platforms, especially LINUX based ones. Unlike closed platforms (iPhone, etc), You can just copy your program binary onto a SD card and run it on the Pandora like a normal computer. An SDK is generally just a properly setup group of libraries + utilities + toolchains + IDE that you could just as easily download individually.
For Pandora Development:
Toolchain = Any ARM-Linux GCC (ie CodeSourcery) + GNU Make
IDE = What ever you like. I use Code::Blocks.
Libraries = You will be able to copy the shared objects + headers from the Pandora OS. I'm guessing most the Angstrom libraries will be available, others will be download-able as they're ported.
Utilities = There's nothing really critical but if you use OGLES you'll want to grab the PowerVR SDK.
Once the Pandora's released I'm sure someone will package all this into a nice zip that you can download.