According to me the game is near the not growing, not declining mark. According to my experience new players and generation don't like slow games like this and if they want a fast game like this they would instead go for HOI4 as the *2 speed and other maps don't make the game from going on for weeks to going on for couple of days, it makes the time taken to do things shorter. The game is also mind using, and when I show my friends and brothers this game, they sat 1)it is too slow. 2) it is strategic and uses the mind, and they play games for fun, not to use their brains extensively like they do in studies. Thus because of the above two reasons the game will only grow slowly as their are exceptions like I am, who likes only grand strategy games.
It will also not decline as older players who have played for years/ months, are mostly not leaving as playing so many games they start to love/like the game. However it is slowly declining and I voted declining as even old players like me who have played for years are leaving as, the game had only one major 1.5 update. Other minor updates under the 1 and 1.5 version, didn't change much in the game and how it was played. Thus if you count there was only one major 1.5 update, which has now became old.
Here's an example - In the 1 version my plan was always, pick any costal nation, make an equally powerful navy, air force, and land army, made of all units equally spread so that they were diverse and could take down anyone with there diversity.
And, In the 1.5 version, I classify it as major as it changes my, and all players game plan completely.
The new plan was, choose Germany(As it has the most neighboring AI countries-
, Make equally powerful navy, air force and army, In navy only make submarines, In air force make fighters and attack bombers, and anything else if needed, and in army only make Motorized Infantry, SP Artillery, SP AA, Heavy Tanks.
Thus this was the only major updates making me from any nation, any unit player, to Germany and some unit player.
Thus the game needs some major updates like this or else it will slowly decline for now (as now old players are leaving as some of them have seen all aspects of the game and are bored like me), and if a major update doesn't come it will decline rapidly in some time (as more players leave).
For ideas check the suggestions and have many suggestions being added at once.