Researching new military equipment is all well and good I think that there should be other branches such as Economic Research and Infrastructure Research to name a few. This will make the game more challenging in some areas such as trying to balance out military, economic and infrastructure researching, but easier in others such as faster troops movement speeds and more resources depending on what has been researched.

As well as adding new research branches there should be new things to build in non-urban provinces such as Railways and Highways for example, these will allow faster troop transport speeds and will also only allow railway guns to go through provinces with railways, therefore making the game more realistic.

As I was thinking about this I began wondering about "Wonders". These are buildings that you build in urban provinces to greatly increase morale. But, these wonders should be customized to fit the country that they are being built in, So things like The Colosseum for Italy and Sydney Opera House for Australia for example. But these wonders will have to be researched first before you are able to build them.

I've actually read your proposed commander plot and I think that there could possibly be an extra branch of research or recruitment where you can recruit Generals. But I think that the generals shouldn't have massive boosts of defense or attack because they will then be very hard to defeat but overall I think yes, it could go hand in hand with your commander idea.