I think that depends on your players and what they are looking for from the game.
It wouldn't have worked too well with the TT group I ran it for, nor for the PBP group I have at the moment. For both of those groups, too many things going on is a distraction. They can't concentrate on a story line, and they lose the thread of the campaign, and they lose interest. For my groups there has always been an element of fantasy escapism as well.
Certainly, when I am playing, I am not interested in deep political plots, detailed project plans and loads of people management. I do that all day at work. I want a nice simple straight-forward story line that I can follow without too much effort, where I can imagine that I am some weird, wild druid (Other classes are available) :)
Or, in the case of Kingmaker, a gifted Wizard building his stronghold and establishing his line as a noble family ...
It can certainly work if your players are up to it. To me, this is actually one of the main draws of Kingmaker in that it is a very open ended campaign and can be easily modified with changes, additions, etc. I did a similar thing in another campaign (not KM but a homebrew) where the players were given a number of hooks and it was left up to them to decide which to pursue. The idea was to give the players meaningful choices. So in the example here, if the party decides not to intervene in the Brevoy civil war, then they may not like the outcome (i.e. Issia wins and then comes calling on the fledgling kingdom that has "stolen" territory from Brevoy).
As JohnB states though, not every group will appreciate the multitude of options, nor the feeling of being "punished" for not pursuing certain hooks, even if there is a sense of realism to it. I do think that if you are going to go this route, it really helps to have some sort of campaign website, or other form of campaign management, that the players can look to in order to recall events, npcs, etc.
Edit to add: One other thing to consider is how well does your group get along with each other (in rl, not in game)? The problem with throwing a lot of hooks out there (where not all of them can be resolved due to time constraints) is that it could lead to arguments between the players as to what to do first, next, etc. This can become even more pronounced if the players really get into their characters and their backgrounds and thus have a reason not to budge, etc.
Another thing to consider is that the players are the rulers of a Kingdom (or a Duchy or a Barony), and thus have more resources to call on than just their own two hands. If there are several things going on at once that they feel all need addressing, they could delegate trusted people to deal with some of them while they personally address others.
The resolution of a given situation might not be as much in the ruling council's favour if they don't deal with it personally, but presumably it will be better than if they just left it to burn unattended.
I can't recall, pennywit - are you one of the GMs whose players have secondary PCs who run around doing adventuring and exploration on behalf of their primary ruler PCs? Even if not, you could allow them to create lower-level characters to delegate the situations to, and play out all those plots in turn even though they're occurring simultaneously, if you want your players to actually experience all the gameplay you're planning.
The other option is for them to delegate to NPCs. Would you have happy with some of these plots being resolved off-screen by delegated NPCs, potentially invalidating some of your prep? You'd also need some way to determine how successful the NPCs are in their efforts... I'd be inclined to work it out through some sort of roll or series of rolls, so you don't just declare how it plays out by fiat.