Firtsly I want to say how much I enjoy Steel Division 2, It's a great game, well done; however, i cannot lie, i still prefer Wargame RD. I think your next game would have great success if you combine to good things about both games.
Wargame flows very well, I think this is helped by the era it is set in - cold war/modern, the age of mechanised infantry and mobile warfare. I think this is also aided by the grouping mechanic where you can stack untits into platoon sized formations, making it easy to control a larger force.
The Deck system on Wargame also gives the player greater freedom to produce multiple different decks. Understandably SD2 has tried to be as close to reality as possible, and that's great, but it limits the freedom to create different decks. This is such a unique selling point for Wargame. In SD 2 I only use one or two different decks, in Wargame I have at least 15 I use on a regular basis.
A key reason i believe Wargame is so much more poluar than SD2, is the graphics requirement. Steel Division games require some form graphics card, something most non-big time gamers have in their computer. Wargame however, was playable by anyone with access to an OK laptop.
One thing that doesn't work in SD2 is the front line system, it removes all possibility of sneak attacks and removes alot of "out of the box" thinking options. I also feel that the vetrancy system worked better in WG, being able to advance someunits through vetrancy was quite rewarding, and I feel this would wrk well combined with command and leader units in an SD style.
Some great things in SD2 to bring into the next game would be the campaign, this would work great with the way Brigades and Battlegroups work in the cold war era (although I did also enjoy the WG EE campaigns aswell) maybe have multiple different styles of campaign? Also the smart orders and the way command and leader units work, big fan of that.
Suggesting something completely knew, I think having the freedom to choose the loadout of planes and helicopters would be great, have a base value for the air frame and then additional points for missiles etc. I also invision a new game mode, standard multiplayer gameplay (conquest or destruction (or bring back Defence mode!)), however losses in the deck are permenant. After each game you can choose how to replenish or edit your deck, maybe more replenishment points for a victory over defeat or the achievement of bonus objectives during the match?
Keep up the good work!