I'm not sure Great Captain events need be more common; I do like Kgauck's loyalty point. However, I think both DMs and players need to have a good idea of what wars and rebellions look like. Under standard BR rules, rebellions are pretty hopeless things for the rebels, just nuisances to the regents. Seizure of a castle under such new rules makes it a much bigger deal. In fact, any rebellions and Great Captain events that do occur are likely to start with a castle or two, if possible.

As for warfare during the seasons, I agree that this is something greatly lacking (for obviously rules simplicity reasons) from BR rules. Then again, the lack of harvest times and so forth is also something of a problem. This could again be handled by variant rules. For instance:

Summer (south of the Aelvinnwode and similar lateral line across Cerilia): Add 1 to movement cost of travel unless it is along a river or highway (heat exhaustion being a problem). North of this point, no change.

Fall (if optional logistics rules are proposed): Forage alone can sustain armies for twice as long without supply chains (4 weeks)

Spring (again if optional logistic rules such as outlined previously are in play): Forage can only sustain units for half as long (1 week)

Winter: Subtract 2 from all morale ratings. If snow or blizzard during the week, all travel shifts one step to the left on movement chart (highways act only like roads, roads like trackless, trackless become impassable to armies). Units in fortifications ignore the impact to morale.

Depending on how detailed you want to get, there would also be strategic modifiers for special terrain (desert, tundra, mountains), and of course soldiers fighting our of their normal climate would suffer the penalties outlined in BRCS tactics (Anuireans are not used to a Rjurik winter). I don't think terrain is different enough in Anuire to warrant additional complication.