A funny sealed league idea would be to play using ante. The league can go on indefinitely, until players that no feel they no longer have the resources to construct a playable deck (or want to keep their remaining cards) concede.
You may change your deck between rounds obviously.
The most fun league I ever played in used ante. This was back in Ice Age and we got (I think) 1 starter deck and 2 boosters. There was no added land; you had what you had. I was running two mountains in a WB deck, because I didn’t have the plains/swamps to fill it out. The drama of seeing one of my swamps up for ante was intense, since I didn’t think I could keep running black with fewer. A league where losing/winning games could make you totally shift your deck was amazing.
Wizards Jay
The most fun league I ever played in used ante. This was back in Ice Age and we got (I think) 1 starter deck and 2 boosters. There was no added land; you had what you had. I was running two mountains in a WB deck, because I didn’t have the plains/swamps to fill it out. The drama of seeing one of my swamps up for ante was intense, since I didn’t think I could keep running black with fewer. A league where losing/winning games could make you totally shift your deck was amazing.