this is a bit of a different suggestion but it just popped into my head and i thought i could be interesting to discuss (if not see in the game one day)
a player can commit some of their forces (works like an attack?) to kingdom defence - that is, defending all the provinces in the kingdom. works as force defence points / # of provinces in kingdom is distrubted to each individual province's defence points.
it would appear in the KD news as "x sent an expeditionary force out in defence of the realm" and have duration equivalent to you attacking your own province (14-16 hours?).
with anon it could read "an unknown force has taken up arms in defence of our kingdom", thus making it harder to tell who has dispatched troops, same as current anon attacks...
casualties would be inflicted on the force based on the number of hits taken by the KD as a whole over the duration of the comittment.
this could be of use to a kingdom that has a significantly larger player (ie a TM) that is otherwise not contributing to the KD military effort.
other than that it may not be particularly useful for everybody.
i can't see it as being useful to a bank as any commitment of their forces just makes them easier to break, and considering their draft is already super low it just doesn't make sense for them unless they raise that draft substantially.
another alternative to aid may be "Send Detachment" that works in a similar fashion to kingdom defence but is targetted at a specific province, so a player could send forces in defence of another province but leave their own weaker for the duration of the march.
not sure how it would show up in the SoM, but in the SoT it could just be a simple addition to overall DPA with the defence points of the detachment being calculated as per the military effectiveness of the recipient province.
just a few ideas!