These are some ideas from a player's perspective, so some of them may not be good ideas from the perspective of a modder.

I think BGR-V should be part of every submod, at least as an option. Some people may not agree Obviously either they have not played it or they come from a different planet!

Just kidding, anyway, all ideas are welcome.

1) Rebels:

Rebels should be revamped to be a lot stronger and numerous, with more general-led armies, as opposed to weak 3-4 unit stacks that players can often ignore for a long time. They should be more active, spawning more units as they captures cities, and posing a serious threat to the player's faction, one that can potentially kill off your campaign.

This is not just to reflect the historical fact that almost all factions at the time had to continuously deal with rebels, but also to make the game harder for larger empires, making super massive bubble factions an unlikely occurrence, as they should be.

Of course the main problem with this proposition is that the AI, already at a disadvantage to the human player, will have the extra burden of dealing with rebels. The key point here is to link rebel probability of occurrence and strength to how large the host empire is. This way small AI empires will not be hurt.

Large AI empires would tend to shrink, wouldn't that make it easy for the human player?

Not if the Rebel AI has its priority shifted towards attacking the human player. Then if rebellion spreads in a region, the human player should be the first to be concerned. This has to be tested to measure how well the AI does.

2) Governor's Rebellion.

Should become a frequent occurrence for nobles governing rich, big settlements.

However, at the moment, the game always prevent nobles from turning into rebels if they are governing a city. The ridiculousness of this is obvious, so no need to explain how the opposite should be true.

The problem is that when a noble's loyalty drops too low, the population revolts and he is kicked out.

That's not the same thing as the noble himself breaking his ligeance and defying the king.

Apparently this is not easy to implement, but I have a suggestion that may very well be silly and impossible to do: Can the game be altered so that rebels offer bribes to governors under the table? (invisibly, without diplomats).

If this can be done than it's automatic that lower loyalty governors will have a large chance of rebelling.

Enough of rebels and rebellions.

3) The "Stripped of Titles" trait.

I suggest a way to add difficulty to the campaign. Re-introduce the "Stripped of Titles" trait, with a stronger effect. It can be so severe that stripping a noble from ownership of a region can make him forever disloyal (not entirely unrealistic).

In this case the player's hands will be tied when he is trying to manage a big empire, slowing down his building and recruitment significantly.

4) Killing your own nobles.

How about a trait called "Marked for death", which is triggered by dropping a "Marked for death" ancillary on the noble. The king wants this noble dead.
(perhaps something related to (3) above? the player wants to free the deed ancillary for a certain settlement without dealing with the unrest that comes with that).

The noble has a chance of dying next turn (perhaps in an act of god, scripter's opinion needed). If he's killed, the king could get a trait similar to "offends the nobility", or something along these lines to make it a risky decision to kill a noble.

5) Naval invasions:

are better than before, but still not effective enough. Ideally, the AI would have no problem staging naval attacks. This has the potential of giving real teeth to coastal AIs. Some AI factions should be able to use navies to get their Crusading armies to the middle east.

I believe this involves solving some complicated coding problems.

6) Reputation:

Something should be done about the effect of reputation on diplomacy. It may work well for European factions, but for an eastern faction which is at war with 16 European factions over a crusade, an alliance with other muslim factions should in fact become easier.

(In my current campaign as the Fatimids, the Seljuks would not even consider my peace offer even though: I have outstanding relations with them, we share the same enemies, I am completely dominating the field, and I'm offering a very generous offer )

7) Family Members vs. Generals:

The game allows for two types of nobles, so why not use that?

They could have different abilities. For example, family members could be made rich and capable, while generals more loyal and better at commanding armies.

The quality of suggestions is plummeting as you can see. So I will stop here. Any ideas from other BGR enthusiasts would much appreciated.