An approach I have been working on might satisfy both Rowan and bbeau22.
Basically, everything remains class based as bbeau22 suggests, and I think his argument is compelling. However, Rowan is right, 4e is not a multi-classing environment, so to have both adventuring and realm abilities, characters need extra abilities to manage domains.
Ultimately, that means deciding what kind of ruler a character should be at some benchmark locations, say 1st level, 5th level, 10th, 20th, and if one desires, beyond. Then create a pattern of abilities that produce that end result.
Because the power-up at each level in 4e remains profound, I prefer to maintain a low level environment for BR. Tentatively, I remain structured around the range of class levels typical in the published materials, so that the top rulers will be just beginning their paragon path, and characters at the end of the paragon path will be diminishingly rare. Based on the feel of things, I am slightly increasing the levels of characters, just so that the top end is no long my 3x standard of 10-12, but more like 11-14. Basically, Aeric Boeruine becomes a 13th level Warlord, instead of the published 12th level 2e fighter, or a Fighter 4/Noble 8 in 3e.
There are two tracks of abilities for domain powers, one is a standard every regent needs this stuff package of abilities, like the ability to attract dedicated cohorts, followers, and contacts, recruit lieutenants, perform court ceremonies, Iron Will, stuff like that. Then there are talent trees so a regent can focus on diplomacy, administration, finance, warfare, espionage, trade, rapport (what we would call public relations), and such abilities. Each talent tree is intended to have roughly a six level arc, so that a 13th level character like Aeric Boeruine has just picked his first power from a third talent tree.
Third, is a path of blood ability power-ups. So every character gets their starting blood abilities, plus blood mark and blood history. All of these powers are weak, almost tainted at 1st level. The 1st level version of Aeric Boeruine does not have the full strength version of Battlewise that impose the kinds of problems that made ECL an issue compared to the character that had Animal Affinity, or something like that. Instead the 1st level character who selects Battlewise can effect one unit with a minor bonus. Every three levels you get a blood ability power up. You can’t select the same ability to power up consecutively.
A character like Aeric Boeruine, might have selected Battlewise twice (at 3rd and 9th levels) Bloodmark at 6th level, and Anduiras’ Resistance at 12th.
The result is that a character gains realm abilities, and has a distinct class identity. In a sense, everyone is automatically multi-classes as a noble (which is pretty much how I built 3x characters), and commoners get the same thing, but based more on the idea that everyone is multi-classed as an expert in some profession.
A commoner fighter might select weaponsmith has his “profession” and get get abilities that allow them to master that “domain”. So they can attract apprentices, make masterwork items, join a guild, derive an income, operate a workshop. Their life outside of adventuring. What do they do between adventures.
So that’s my idea, and I will post on it further as I get more of it worked out.