I guess that you have seen this somewhere else, but in case you haven’t: there is a page with all current HP calculators’ emulators for PC, in HP’s French site. You can find it here:
You have several surprises awaiting there:
Both the hp17bii and the hp42s were built on the same Saturn architecture, and therefore, if you have mastered the emulator architecture, it would be a piece of cake to do the emulator of the hp42s. And why not think about doing another limited edition…?
I have been told by hp officials that the current HP17bii is not a good platform to do that, since it is built from scratch on a completely different architecture, and it is not even compatible with the original HP17bii firmware. But this is a good development thread - the really good thing about these calculators was its wonderful set of features and clever key combinations.