ok if you require an answer I guess no one else will do it, so my answer is:
"10 minutes for PvE, just like it is today, and 7 minutes for PvP" PvE can be completed under 1 minute, did you try rPvE diff 1?
"The quest can require two matches just like it is today for campaign PvE but then it should be 100 BFP or more." why quest requirering 14 minutes should give more than all other quests that was supposed to take 30 minutes each with some overlaps (unfortunatelly the reality is much different )
"I also think that new, and more involved quests that give a booster as a reward would be more exciting." do you have an idea for quests that will not make gap between skilled players and unskilled players even bigger?
"Play 4 ..." play not win? so it can be done under 1 minute by skilled player? But it can also take over 8 hours to someone not trying to exploit it?
"In that scenario it could be 6 matches with different 6 deck combos" so changing 1 card?