I agree with this idea. Probably by a stroke of luck I haven't had a lot of games where too many people went AFK, but I too have one game where all my efforts might go to waste because I'm the last of 6 players remaining. Strangest thing is that most even built up +1000 armies before leaving while the average AFK'er tends to do so on day 1. But most people don't have the luck that the leavers leave empires that take days to crumble. But regardless of when they leave, one player doesn't stand much change against a situation like this:
And that's just one sixth of the map, the rest isn't much better and I'm unfortunately right in the middle. Freaking deadman's land everywhere, though only half of it of the immortal kind. (I know it says there are only four AFK, one recently returned but I doubt it'll be for long.)
Taking that game as my experience, the 'governing' option would indeed be the most practical solution. The ability for the active players to temporarily claim settlements and train the people there would be a necessity. Right now, the settlements I do have are starting to run out of living souls and I can't get do anything with the hundreds of mortals sitting there doing nothing. I have to either watch the undead run over unprotected fortresses or send my own already thin-spread soldiers whole days in advance to protect them. And that's just impossible to keep up.
I don't think the remote control thing would be wise, though. This would indeed be a 'first come' mess and would make the active players too overpowered, especially when combined with sharing resources. Probably wise to keep the Valour costs (to trade settlements, not to recruit them) and let the AFK'ers keep their troops as well.
Sharing resources would be a necessity though, you can't expect a player to run six empires with only one empire's income. But if a player were to lose all their gold to the other players the moment they go AFK, this would be too much of a motivation for people not to come back at all when they do go AFK. I can imagine not being able to play for a whole day and then considering all my open games forfeit because others would have taken my gold and valour.
So what I suggest instead is that the income from AFK players is pooled together and then spread among the active players. That way, a temporarily AFK player doesn't lose anything and the active players get a bit stronger to compensate for the inactive ones. Just a little bit if it's just one, a lot if everyone else went AFK.