Clearly there's a pattern they've been following with the events to date, but personally I am hoping they have some more ideas up their sleeves to change it up a bit.
Here's an idea for an event I'd love to play: What If?
"What If?" was a series from back when I was collecting wherein they took a major storyline arc and looked at what might have happened if something went differently. These stories were outside the regular continuity, and were often a lot of fun.
Here's how I'd set up the event:
1. For the duration of the event, cards would be fusable with other cards that are not the same card resulting in specific combinations (similar to combos for attacks) and the fused card would be something entirely different. For example, one might be able to fuse Bullseye and Elektra for a card showing Bullseye's murder of Elektra. This resulting card would be useless outside of the event.
2. These cards would be able to be sacrificed to open up small questlines. For the above example, perhaps sacrificing the Bullseye Kills Elektra card and a Daredevil would open up a short questline "What if Bullseye Never Killed Elektra?"
3. Rewards could be in the form of special versions of cards resulting from completing certain questlines, or the usual shard distribution if they're lazy. Also, a currency would be devised to track quest progress overall to rank players for the overall rewards.
Essentially, part of this works like the mobile app/game "Alchemy" where players need to determine what can be combined with what and for what result. Since the Fusion controls only display fusable cards, players wouldn't have too difficult of a time discovering combinations, though some combinations may involve cards of greater rarity (thus taking some rarer cards out of circulation after they get sacrificed). More difficult combinations would yield better quests/rewards.