What i expect will happen is that this card will not get the proper testing it deserves and will become a sleeper card because everybody has considered using it but no strong deck evolved from it (cause no one's actually testing it). This happens more often. 2 camps take a stance for or against a card and until the card is proven, the naysayers disregard the potential of a card simply because the burden of proof is with the people that do like the card. This happened to Jace, The Mindsculptor as well and you can still look that up in the original thread I posted
I have a strong feeling that this is just the road most cards take in the process of being acknowledged. Nothing wrong or bad about it.
On topic AND from my perspective as a 'fish' player; all your creatures (and with creatures I mean canonist, teeg, MM, true believer, and the likes...) have the flash ability that Aven Mindcensor has. Now I have learned to be more critical but this idea does give me the sparks to go test out some designs. Lot's of things crossing my mind because I did a lot of building with all kinds of different colors, types with fish. For example the ESG's and the red counterpart in combination with the flash ability that this Leyline would provide could enable a lot of reactionary tempo plays at the cost of 4 slots. I can't really anticipate if it is worth it though.
EDIT: Leyline of anticipation could replace Aether Vial cause they both are bother on turn 1 anyway. Sure they play out differently but I think the 'flash' ability was always one of the strongest assets anyway. That is what Leyline of Anticipation is for Fish, it gets the flash component of vial on board at turn 0. You can't go faster than that. Maybe that green Leyline and this one could be used in Fish at the same time. The slots you will use is Vial itself and things like Shusher. I like the line of Bruizar were he states that these Leylines 'upgrade' the power of your cards in the deck substantially. I agree with him. It should not be that hard to cycle those extra leylines in the mid game with some kind of ability that requires pitching or discarding.