iirc they are skipping to gen 5 first because from a programming & project managing standpoint it makes a lot more sense to jump to gen 5 and then later implement gen 4. This way they get all the hard work done up front and then later it'll be easy to add sinnoh (if they decide to at all), rather than doing all the work to jump to gen 4 and then again when adding gen 5. Theoretically this way we will have both in a quicker amount of time, but in practice who knows. Either way from the differences in the previous PTS and this one it looks they are working their asses off.
Onto a more relevant note, it looks like the PTS is now closed:
RIP HYPE (& my shinies)