2. Why C++ yuk!? If you used Scala (3 times less verbose than Java), and stub in C for performance only where needed (through the JNI), then I might contribute coding (maybe even for free) instead of creating my own altcoin. No way I am going back to 1990s with C++. Been there, done that.

If I were doing it, I'd want to do the bulk of the implementation in bitcoinj of course, just because that's what most users are going to end up using (given current trajectories). It also has the advantage that using a managed language like Java eliminates entire classes of security holes, always a concern when writing financial software.