Oh, I absolutely agree, don't wait to start writing great programs! But, assuming the SDK is released fairly soon, it'll be better if we can avoid using unofficial names and terminology,
particularly in a program like Calcsys. In any case, there are still some serious issues that I need to deal with before it's usable, and at the moment I have two other TI-related projects (TilEm and TILP) that are a higher priority.
As for app signing, the word is that RabbitSign should work just fine if you can arrange to have an appropriate certificate installed, or if somebody somehow managed to obtain the necessary private keys.
With the current version of RabbitSign, you may have to manually specify the program type (since it doesn't recognize the .8ck extension or the 0F product code); I'm planning to release a new version of RabbitSign shortly that fixes those issues.