I read on this thread someone mentions doing some battles for the Vikings to help them ... that would me vvery Cool ! And for those that prefer trading, give the choice to battle or to trade ...
Let's say something like this : a nice challenge (?) .. and IF the player succeed he / she get some extra nice reward
a) battle : a 4 wave battle, starting with 2 enemies, then 3, then 5 and at last 7. If you get through 1 wave give a small reward, going to 2 wave more, and so on! And you can not use diamonds to heal a units between 2 waves
b) trade (negotiation) : 4 negotiations, starting with 3 diff. goods (cult goods + copper coins ( perhaps also supplies and coins?)), then with 4, then 5 and at last 6, BUT here you get each time 3 turns and you can NOT buy 1 extra turn with diamond or via tavern!)
And IF the player succeed he / she get some extra nice reward OR ... another idea, just an "idea" :
if a player did not finish a Setttlement "in time" to get the best End Reward (6 fragments of Runestone), they can try to win this 4 wave battle or 4 wave negotiation as Quest 21 ...
That way they've a chance to win some extra fragments of the runestone, but it's a one way challenge, you get no second chance to do quest 21.
Probably this idea needs some more "fine-tuning" ... I'm not a programmer so do not know what is even possible or not ...
PS : Quest 21 Extra End Challenge appear for every player, but the reward is different !
For those that ended "in time" to get 6 fragment, they can win (for example) some "extra" fragment of a Shrine of Knowledge or something like that), all others can win a mix of both and those that miss the whole "time reward" get a chance to win between 1 and 4 fragments of runestone, depending on how far they get on quest 21 ;-)