The complexity of the game should come from the deep simulation and game mechanics at the core of the game, that are easily accessible to all players. For that reason, Victoria 3 will have a beginner-friendly UI.
One of the more challenging areas of the game is to clearly give feedback of a value’s change over time. In a game with as many interlocking systems as Victoria, giving feedback on how something has changed over time becomes an essential part of the game-loop. How can the developers take several values and show you exactly how it has changed over time? You guessed it, line graphs.
In most cases in Paradox's previous games, you have to tick the game in order to see the effects of things. In Victoria, developers try to make all the immediate effects of your actions available the second you take them.
When taking actions that have consequences spreading far and wide throughout the game's systems, it can be really hard to parse if this is a good idea or not without excessive use of spreadsheet software. So the game predicts things for you.
For example, the Building panel provides you with all the raw building data you could ever need, for you to analyze however you like. For whatever action you may desire, the game provides support in your calculating endeavors with predictions such as the Weekly Balance when changing Production Method and predicted Earnings of the building if you were to expand it.
This will make the game more user and beginner-friendly, by not requiring you to become a statistician just to play it. Though some die-hard fans may take that as an offense.