The only problem
Riot isn't planning Blitz to be a temporary thing (Infact, they're looking for something more Permanent)
Urf was Polarizing, Be it in either ARUrf, Normal Urf, or Draft Urf. Polarizing games aren't all that good for longer-term game modes because, Well fuck, Same reason games like HotS flop. Yes, people will love it, But a lot of people dont love it because what skill expression there is will be drowned out by team equality.
Ascension.. While interesting in concept, It creates the same problem as a lot of hte other game modes of "Play it once, And let it be done", And anyone playing it more than once are trying other champions or are trying to find a meta.
Blitz Atleast has the benefit of being Random enough that no two games are going to be exactly the same, And the only real problem is that a lot of these "Events" Are overly generous on the rewards. The meta will eventually reach a similar meta to SR, But there's also a few meta's that COULD Be designed around abusing events.