I'm not over-estimating people that care about blitzball. I make no estimation after all.
You may or may not believe it, but people WILL be attracted to fantasy sports IF they are well made. And this is what I am saying. If they make a GOOD blitzball, it will have massive replay value like every single other sport game out there, from racing games, through fighting games all the way to...yeah...team sports like soccer or basketball. If they'll give it the mini-game treatment that is to be made and forgotten, aka. make it with linear advancement and little to no strategy, then it'll be dead on arrival. It's not blitzball itself that matters here. It's the idea of a ball game played in three dimensions with special moves attached. Heck, original blitzball was two-dimensional. BUT the special moves are what makes it.
You may not know it, but there are multiple LARGE franchises that just that. A small variation on sport games known to man with added super moves. Look at Technos games (Ike Ike! Nekketsu Hockey Bu: Subette Koronde Dairantō, Kunio-kun no Nekketsu Soccer League, Nekketsu Street Basket: Ganbare Dunk Heroes and some other), Inazuma Eleven franchise, Blood Bowl 1 and 2. Blitzball is the very same concept. Taking something that is well known (a team-based game where the goal is to put the ball inside a specific area, goalpost), with specific rules for handling it (only with legs, only with hands, only by dribbling etc., with or without contact allowed etc.) and adding a non-realistic element (violent or outright impossible attacks that would cause long-term damage or death in real life). The concept is both simple and fun. It's all in the design. It can be crap or "the new best thing". I'm a realist so I don't expect it to be more than a fun little time-waster here or there for most players in the best case scenario. But that doesn't mean that blitzball itself is an inherently flawed concept that cannot be popular. It can. It's just that it will not be nearly fleshed out enough to have the chance for that.