Games: Stellaris: Utopia (release on april 6) or WoW Legion (maybe with a sixty day game card?)
Idea: Insect warfare. When I started playing RTS games at a young age I envisioned a game which would have several unique, base factions, based on insects. You would have to gather resources (leaves, the ... things from pine trees, the long thin things I honestly have no idea whatsoever what they are called, pebbles, and so on), and build your base. Some would have bases underground, some above ground, and some in the trees. The maps would be gigantic and extremely detailed. I didn't think about 3D (I probably didn't even understand the term, northern swedish farmboy 4 lyfe), but it was important you have many different levels to play on. And you should be able to do essentially anything. Ants climbing trees, attacking bees and so forth.
Also, the map. There would be a world map which should look like a map with countries in them, but it would only cover a small area of woodlands, or a single hillside, or something like that. That would be to show you the extent of your kingdom, and from there you could direct things as well. I wasn't clear on what I wanted, but I wanted to use that map. And there would be a detailed map, like your normal RTS map. Later I played Total War and realised that was what I wanted, but more details and seamless zoom between the modes and basebuilding and the diplomacy/nation map would just be the strategy map but really zoomed out.
And, the different factions, or kinds of insects. War would not be the only option. You would be able to conduct diplomacy as well. I was really big on history at this point in my life and backstabbing and spies would be a part of the game, but I had no idea how to implement it. How can a bee spy on ants? It didn't make sense, but I envisioned some kind of pacts being made between the factions. Also you would be able to exchange genetic material and slave races.
So, genes and slave races. The base factions would be just that, very basic. But a part of the fun would be in finding other nations/wandering spiders and either enslaving them (ie putting beetles to work as workers or walking battleships) or using their genetic material. There would be a system in place for creating new units with different parts of insects. That would be a smaller portion of the game though, I mainly envisioned capturing and enslaving (I honestly did not think of the beetles as slaves, but now when I write about it yes, they would absolutely have been slaves) other species. This BTW is part of why I absolutely loved Impossible Creatures, because it took a part of my childhood dream game and made it real.
This was in the mid-late 90's, so ... impossible, to say the least. Hard to do even today. But for a long time I looked at the tiny bits of the world and thought about that game. I have forgotten a lot about the ideas I had, but I know that a lot of them got realised in the Paradox grand strategy titles and Total War, but it has never been quite what I wanted. Think Europa Universalis combined with Total War and Alpha Centauri, with Starcraft, Dwarf Fortress and Aurora thrown in for good measure.
EDIT: Oh yes, and I wanted it to be realistic. I mean really realistic. The insects wouldn't be magical fire-breathing monsters (Starship Troopers), but actual, proper insects. Hence the small/subtle impact of genetic engineering. And physics would be realistic, and things like wind and humidity would be important, because they are to insects. So yes, probably still impossible.