I have to say I'm also quite glad to hear Vic2 is still on Paradox's radar. I found CK2 diverting for a short while, but I've since been drawn back to modding Vic2 again simply because I enjoy the game so much.
I tend to resist adding my voice to the string of "what I'd like to see in the future" posts, as from a developer's perspective it must end up sounding like the fans wanting everything and anything-- and a pony-- but for my two cents:
* Expanded diplomacy. In particular, it would be nice to see the AI using the same diplomacy options to which the player has access-- in particular, the ability to call in allies after the war has started and providing funding for allies. It would also be great to see different levels of alliance, like a "guarantee of independence" (meaning "I'll help you if you're invaded, but I won't help you attack someone") or a more iron-clad factional alliance where the countries are obligated to go to war and cannot choose to drop out (especially useful when dealing with fickle AI allies).
* As mentioned above, a reworked military system. In particular, the warscore system needs some work-- how many times has someone complained that large countries such as the UK and Russia are almost impossible to gain warscore against without going to absurd lengths. You can occupy all of Siberia or India and gain very little warscore... or gain a lot just by defeating a few armies, regardless of those armies percentage of their overall force. CK2 made some excellent innovations in this regard. In addition, more intelligent AI use of seaborne invasion and assistance of allies would be ideal.
* Splitting up national cores into cores (a culture's homeland) and claims (land a country has recognized claims to, but which is not considered integral).
* Reworking the rebel system, both in terms of how pops become part of rebels and what they're fighting for. Right now it's too common for a liberal, educated pop to decide what his democratic country
really needs is an absolute dictatorship. Nationalism-- an important part of the era-- should also be punched up. It would be excellent to see different levels of disorder and/or guerrilla warfare, and rebels being harder to deal with than mole-whacking rebel armies that rise up.
* Changing the vassal system. Sub-states were added, which are nice, but they're just vassals that foreign countries can take chunks out of... and vassals themselves are still rather useless. It would be great to see things like tributary states (they grant a portion of their income to their owner, like with reparations) and the AI actually being able to deal with a vassal on their border (they don't tend to use "Release Puppet", for instance).
* Insofar as new scenarios, I'm not a big fan of those-- and I imagine they're also incredibly hard for the developers to set up and support due to all the changes needed to pops and military units and countless other changes such as tech and literacy levels. If one was to be done, a WW1 scenario would be nice... but only if some of the above things like factional alliances and warscore changes were also done. It would be disheartening to start WW1 and have the UK peace out after two months or have the AI sending sea invasions against colonies rather than actually fighting on the continent.
Not a big list, right?
Whatever Paradox gets up to, they'll have my support. Thanks for a great game.