So i haven´t found it yet… my idea would be easy:
With higher levels you will get higher contracts, but in the worst case you don´t have the time to finish them and rerolling will be expensive at some point. If you play multiple chars it might even get worse since you´ve to decide where to spend your time on.
But since we´ve “tiers” in them already like “finish 15 missions” or “finish 25 missions”, why not combine them?
Just let us roll those 25 missions and if we´ve finished 15, we already get the rewards for it.
To make it even a bit more player-friendly, split the 1000 from the weekly rewards in tiers too.
So let´s say we split the mission in 3 tiers. If you´ve either finished the tier 1 progress on all 5 contracts or like tier 3 / 1 / 0 / 1 / 0, you´ll get the tier 1 bonus, and so on… I guess you know how i mean it should work.
Would be atleast some kind of progress even for players with a life. 
Dunno if it works that way, but does progress carry over from week to week? Read something like it. With the changes above, it should actually be changed to not carry over of course.
Also i personally think that contracts should be locked on difficulty 3 or higher. Having high end players farming them on difficulty 2 is really no fun for newcomers. On top please take care to have always atleast 1 mission with grims and 1 with tomes available on malice or heresy.
Today there have been times with 4 dif. 1 missions, grims have been mostly on uprising, meanwhile only 1 malice mission without anything, but 2 heresy ones both with tomes. Damnation has mostly one of them so, but i guess malice and heresy will be the most played difficulties.
It´s just a bit annoying to be forced to play on a real easy difficulty all day long or gamble on the highest one, because there are only grims available on uprising or damnation.
PS: Please stay away from dailies… being more a less “forced” to login everyday sucks, especially if you might have only time for 2 runs and they fail. Not to mention that it would change the gameplay experience for the worse, if all do nothing but hunting their dailies day per day. (For example lower playercount on heresy / damnation than usual.)
I would actually prefer such a tier-based weekly system.