I feel like this might have been posted before, but I've kinda dreamed of a true 'grand strategy' game. No, not like EU3 or whatever.
Let's call this "Aspirations of Greatness".
There are 3 (up to 5) distinct 'levels' or 'styles' of play.
1. Traditional grand strategy: You rule a realm. You no longer have time to handle the petty squables of your lords nor to command most of your armies - instead you delegate, politicize, plot, and negotiate. You also handle the allotment of resources and funds from your grand treasury to others. You may provide general advice or directives to your lords. This level plays probably somewhat like EU3 or maybe CK2, but in real time.
Optional sub-level: Advisor: Perhaps through personal preference or through being absorbed into another's kingdom, you serve the ruler in some fashion. Maybe you handle all the negotiations. Maybe you just come up with advice while secretly plotting in the background.
2. Mid-level strategy: You rule a province or an army. Possibly both. You are the lord who squabbles with other lords, and you also have to make sure your requests to the ruler and your requests of your generals get paid attention to. You mainly concern yourself with provincial level politics but you you also have to worry about the crops and the economy in your region. Depending on how much control you have over the local politics (I guess 'how big your province/army is') this might play again like a subsection of EU3 or CK2, or more like an RTS game.
Optional sub-level: Mayoral or city level or an army: Direct delegation of economy and crops in your area. OR commanding a bunch of local troops. Politicking with other mayors for the advice of your lord, or subterfuge against them somehow. RTS level play.
3. Low-level strategy: You lead a small section of troops or people. Maybe you farm. Maybe you run a shop. Maybe you are in command of a small section of army units. Nonetheless, you take orders and you complete objectives in real time. Of course, you could rebel, but... Plays very much like any top-down or squad based combat game.
In terms of play: 1 commands all 2s in their realm, 2s command all 3s in their realm. 3s appear as 'hero units' in 2's vision, and 2s appear as 'governors' or 'generals' and their groups of 3s as armies to 1s.
So in essence: 3 (or 4) tiers of gameplay, changing from squad-combat to RTS to EU3 - all in real time - as you start delegating over more and more regions. Of course, the difficulty is synchronization (probably heroes and generals style, but with the added 'grand strategy' tier) and making everything fit together in a coherent way. Especially when you throw in the fact that combat is being waged between multiple rulers of realms simultaneously, each of whom have governors who may change hands at any time.
I mention things like farming, shopping, etc, because presumably there must be an economic aspect as well, and I assume there are gonna be some people who want to be farmers. But I guess the primary draw of the game would be the strategy and combat aspects.
A single player mode might work well starting you at Tier 3 and allowing you to prove yourself and amass enough followers to eventually grow to Tier 1. Of course, you could also lose everything at Tier 1 too, so it's not all about growth - one lucky assassin or coup is all it takes...