I think making a year last 80 days is pretty brain-dead, myself. That means 10 day trip takes 1/8 of a YEAR! It means that for every day that passes, 4.5 days have passed.
Why not actually have some interesting dynastic gameplay...? All the people in favor of this idea don't seem to be suggesting anything interesting be done with it. Probably because they know TW is not going to having anything remotely comparable to a 4X game, and this is going to end up a very forced and tacked on feature.
One way they could try and do this, fairly simply, is make combat a lot more rewarding in terms of cash, but have a lot more risk in terms of getting debilitating wounds that cripple you for life, for example. After you get a few of those, you'll decide to take your money and retire, which inevitably leads to you being succeeded by your son or younger cousin or whatever, with most of your stats and without the wounds.
...Come to think of it, what happens to the story quest, if we take too long about it? Will the kidnapped children be elderly pensioners by the time you reach them?