Knight at Arms
Agreed. What he mentioned was very similar to the messenger mod that someone made for BL. You basically "sent a message", and after three days after the "message arrived" you spoke to the lord telepathically. It is unfortunately immersion breakingPersonally, I don't like the idea of this method. Not only is it an immersion killer, but the many fears that you mention seem like interesting fresh gameplay to me.
I mean, if the lords of the realm are incapable of meeting at the capital to discuss kingdom matters due to them being occupied defending their borders, it gives the impression of "we will discuss who gets x fief or y policy once we subdue our enemies" which could lead to instability if much time occurs between meetings. The catch, of course, is if they still decide to hold this meeting while at war, there could be consequences since the most powerful figureheads of the faction are indisposed while their enemies loot and siege their lands. Apply this to every faction, and this mechanic can give more power and responsibility as a ruler, as you/they would decide if the risk of holding a council mid-war would be worth it to figure out fief distribution/policy management/international diplomacy. This would also heavily benefit non-warring factions as their free agendas would allow for them to arrive at the council, discussing the many needs of the realm and overall allowing the ruler to appease his vassals and prosper the people (feast?).