Vicky 2 is awesome, and one of my favourite PDS games to date, but as everyone else has posted, there's soooooo much that could be improved. Just the idea that anyone (even PDS, bless their GSG souls) could get that time period 'right' in the second crack, AI aside, is expecting a bit much. Key things that could be improved substantially are:
- Diplomacy. It's pretty solid, but there have been big steps forward in EU4 that Vicky 3 could benefit from (and build on).
- The Economy. Vicky 2's attempt was great, and by the Heart of Darkness was starting to come together, but there's a heap of potential to polish and improve this, both in terms of its functioning and interface (which was a bit step up from Vicky 1, but it's a very tricky thing to get right).
- Starting dates. It's surprising there's no September 1914 start date (or even a 1912 start date), and it wouldn't be bad to have one prior in 1870 (Franco-Prussian war) and 1904 (Japanese-Russian war) as well. Best possible would be an EU/CK post-1066 style 'start whichever day you like' approach, but that may be too much work to be practical.
- Warfare. It's solid, but for a game that covers WW1, could be done better. That, and the naval DD for HoI4 has some great ideas that could work well in a new Vicky.
- AI - the most important thing in _any_ GSG where you don't have humans playing every country (which in a Vicky game would be a lot of humans in the game!) Vicky 2's AI was a good deal better than Vicky 1's, but improved processing power and better AI algorithms will always be good - we're a long way off the "AI improvement curve" having a shallow gradient.
And that's off the top of my head

. To be honest, the PDS game that feels 'most' complete would be CK2, so if there was any game for which a sequel could be questioned, that'd be the one (and I'm not suggesting it isn't necessary, just that it's 'less' necessary than Vicky 3 - I will buy and play CK3

)