The addition of elite streaks in the game has been great! You can level up much faster, people always want to do quests on elite... But therein lies the problem. No one will do quests on a lower difficulty because it breaks their streak. And if it comes to a choice between breaking the streak and not doing the quest, no one will do the quest.
This was particularly brought to my attention today, when we did an elite von5 with the intention of doing an elite von6. However, right after we finished von5, one of the healers recalled out and dropped the group. Now, that instantly put elite von6 out of the question. One of the people in the group pointed out we could do it on normal or hard instead, but that would break everyones streaks, so everyone in the group dropped out and we didn't do von6. This is a pain. I personally don't care about streaks, but nearly everyone else does, and people don't want to break their streaks.
So, my suggestion is this:
Get rid of the 'breaking' mechanism for streaks. Have it the same way, so that if you've done it on a different difficulty before you aren't eligible for streak bonuses, but please remove the 'breaking' mechanism. It's harmful to parties and results in a lot of people not doing a quest because they don't want to break their streak.